diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5364a70..800b7ec 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Switched to using `gleam_time` instead of `birl`.
+  - All `birl.Time` usages have been replaced with `gleam/time/timestamp.Timestamp`.
+  - All `birl.Duration` usages have been replaced with `gleam/time/duration.Duration`.
+
 ## [1.0.1] - 2025-07-26
 
 ### Changed
diff --git a/gleam.toml b/gleam.toml
index 485694f..cb6012c 100644
--- a/gleam.toml
+++ b/gleam.toml
@@ -5,10 +5,10 @@ licenses = ["MIT"]
 repository = { type = "github", user = "maxdeviant", repo = "bigben" }
 
 [dependencies]
-birl = ">= 1.8.0 and < 2.0.0"
 gleam_erlang = ">= 1.2.0 and < 2.0.0"
 gleam_otp = ">= 1.0.0 and < 2.0.0"
 gleam_stdlib = ">= 0.62.0 and < 1.0.0"
+gleam_time = ">= 1.4.0 and < 2.0.0"
 
 [dev-dependencies]
 gleeunit = ">= 1.6.1 and < 2.0.0"
diff --git a/manifest.toml b/manifest.toml
index 6a68872..76ce8c1 100644
--- a/manifest.toml
+++ b/manifest.toml
@@ -2,19 +2,16 @@
 # You typically do not need to edit this file
 
 packages = [
-  { name = "birl", version = "1.8.0", build_tools = ["gleam"], requirements = ["gleam_regexp", "gleam_stdlib", "ranger"], otp_app = "birl", source = "hex", outer_checksum = "2AC7BA26F998E3DFADDB657148BD5DDFE966958AD4D6D6957DD0D22E5B56C400" },
   { name = "gleam_erlang", version = "1.2.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "F91CE62A2D011FA13341F3723DB7DB118541AAA5FE7311BD2716D018F01EF9E3" },
   { name = "gleam_otp", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_stdlib"], otp_app = "gleam_otp", source = "hex", outer_checksum = "7020E652D18F9ABAC9C877270B14160519FA0856EE80126231C505D719AD68DA" },
-  { name = "gleam_regexp", version = "1.1.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_regexp", source = "hex", outer_checksum = "9C215C6CA84A5B35BB934A9B61A9A306EC743153BE2B0425A0D032E477B062A9" },
   { name = "gleam_stdlib", version = "0.62.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "DC8872BC0B8550F6E22F0F698CFE7F1E4BDA7312FDEB40D6C3F44C5B706C8310" },
-  { name = "gleam_yielder", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_yielder", source = "hex", outer_checksum = "8E4E4ECFA7982859F430C57F549200C7749823C106759F4A19A78AEA6687717A" },
+  { name = "gleam_time", version = "1.4.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_time", source = "hex", outer_checksum = "DCDDC040CE97DA3D2A925CDBBA08D8A78681139745754A83998641C8A3F6587E" },
   { name = "gleeunit", version = "1.6.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "FDC68A8C492B1E9B429249062CD9BAC9B5538C6FBF584817205D0998C42E1DAC" },
-  { name = "ranger", version = "1.4.0", build_tools = ["gleam"], requirements = ["gleam_stdlib", "gleam_yielder"], otp_app = "ranger", source = "hex", outer_checksum = "C8988E8F8CDBD3E7F4D8F2E663EF76490390899C2B2885A6432E942495B3E854" },
 ]
 
 [requirements]
-birl = { version = ">= 1.8.0 and < 2.0.0" }
 gleam_erlang = { version = ">= 1.2.0 and < 2.0.0" }
 gleam_otp = { version = ">= 1.0.0 and < 2.0.0" }
 gleam_stdlib = { version = ">= 0.62.0 and < 1.0.0" }
+gleam_time = { version = ">= 1.4.0 and < 2.0.0" }
 gleeunit = { version = ">= 1.6.1 and < 2.0.0" }
diff --git a/src/bigben/clock.gleam b/src/bigben/clock.gleam
index 5defe92..5412480 100644
--- a/src/bigben/clock.gleam
+++ b/src/bigben/clock.gleam
@@ -1,20 +1,20 @@
 //// A clock.
 
 import bigben/fake_clock.{type FakeClock}
-import birl.{type Time}
+import gleam/time/timestamp.{type Timestamp}
 
 /// A clock.
 pub opaque type Clock {
-  Clock(utc_now: fn() -> Time)
+  Clock(utc_now: fn() -> Timestamp)
 }
 
 /// Returns a new `Clock`.
 pub fn new() -> Clock {
-  Clock(birl.utc_now)
+  Clock(timestamp.system_time)
 }
 
-/// Returns the current time on the given `Clock`, in UTC.
-pub fn now(clock: Clock) -> Time {
+/// Returns the current time on the given `Clock`.
+pub fn now(clock: Clock) -> Timestamp {
   clock.utc_now()
 }
 
diff --git a/src/bigben/fake_clock.gleam b/src/bigben/fake_clock.gleam
index cfeee94..45478d2 100644
--- a/src/bigben/fake_clock.gleam
+++ b/src/bigben/fake_clock.gleam
@@ -1,9 +1,9 @@
 //// A fake clock for manipulating the flow of time.
 
-import birl.{type Time}
-import birl/duration.{type Duration}
 import gleam/erlang/process.{type Subject}
 import gleam/otp/actor
+import gleam/time/duration.{type Duration}
+import gleam/time/timestamp.{type Timestamp}
 
 /// A fake clock.
 pub opaque type FakeClock {
@@ -12,25 +12,25 @@ pub opaque type FakeClock {
 
 /// Returns a new `FakeClock`.
 ///
-/// The current time will be now in UTC.
+/// The current time will be the instant the clock was created.
 pub fn new() -> FakeClock {
-  new_at(birl.utc_now())
+  new_at(timestamp.system_time())
 }
 
 /// Returns a new `FakeClock` at the given time.
-pub fn new_at(now: Time) -> FakeClock {
+pub fn new_at(now: Timestamp) -> FakeClock {
   let assert Ok(actor) =
     actor.new(now) |> actor.on_message(handle_message) |> actor.start
   FakeClock(actor.data)
 }
 
 /// Returns the current time on the given `FakeClock`.
-pub fn now(clock: FakeClock) -> Time {
+pub fn now(clock: FakeClock) -> Timestamp {
   process.call(clock.subject, 10, Get)
 }
 
 /// Sets the current time on the given `FakeClock` to the specified value.
-pub fn set_now(clock: FakeClock, now: Time) -> Nil {
+pub fn set_now(clock: FakeClock, now: Timestamp) -> Nil {
   process.send(clock.subject, Set(now))
 }
 
@@ -40,18 +40,18 @@ pub fn advance(clock: FakeClock, duration: Duration) -> Nil {
 }
 
 type Message {
-  Get(reply_with: Subject(Time))
-  Set(Time)
+  Get(reply_with: Subject(Timestamp))
+  Set(Timestamp)
   Advance(Duration)
 }
 
-fn handle_message(state: Time, message: Message) {
+fn handle_message(state: Timestamp, message: Message) {
   case message {
     Get(client) -> {
       process.send(client, state)
       actor.continue(state)
     }
     Set(now) -> actor.continue(now)
-    Advance(duration) -> actor.continue(birl.add(state, duration))
+    Advance(duration) -> actor.continue(timestamp.add(state, duration))
   }
 }
diff --git a/test/bigben/clock_test.gleam b/test/bigben/clock_test.gleam
index ba118ee..7fe9cb8 100644
--- a/test/bigben/clock_test.gleam
+++ b/test/bigben/clock_test.gleam
@@ -1,32 +1,32 @@
 import bigben/clock.{type Clock}
 import bigben/fake_clock
-import birl.{Day}
-import birl/duration
 import gleam/int
+import gleam/time/calendar
+import gleam/time/duration
+import gleam/time/timestamp
 import gleeunit/should
 
 pub fn clock_can_be_faked_test() {
-  let assert Ok(now) = birl.parse("2024-04-12T01:33:46.382Z")
+  let assert Ok(now) = timestamp.parse_rfc3339("2024-04-12T01:33:46.382Z")
   let fake_clock = fake_clock.new_at(now)
   let clock = clock.from_fake(fake_clock)
 
   what_day_is_it(clock)
-  |> should.equal("Today is Friday, April 12, 2024")
+  |> should.equal("Today is April 12, 2024")
 
-  fake_clock.advance(fake_clock, duration.days(5))
+  fake_clock.advance(fake_clock, duration.hours(5 * 24))
 
   what_day_is_it(clock)
-  |> should.equal("Today is Wednesday, April 17, 2024")
+  |> should.equal("Today is April 17, 2024")
 }
 
 fn what_day_is_it(clock: Clock) -> String {
   let now = clock.now(clock)
+  let #(date, _time) = now |> timestamp.to_calendar(calendar.utc_offset)
 
-  let weekday = birl.string_weekday(now)
-  let month = birl.string_month(now)
-  let Day(year, _, day) = birl.get_day(now)
-  let day = int.to_string(day)
-  let year = int.to_string(year)
+  let month = date.month |> calendar.month_to_string
+  let day = int.to_string(date.day)
+  let year = int.to_string(date.year)
 
-  "Today is " <> weekday <> ", " <> month <> " " <> day <> ", " <> year
+  "Today is " <> month <> " " <> day <> ", " <> year
 }
diff --git a/test/bigben/fake_clock_test.gleam b/test/bigben/fake_clock_test.gleam
index 0f9030a..93df8a7 100644
--- a/test/bigben/fake_clock_test.gleam
+++ b/test/bigben/fake_clock_test.gleam
@@ -1,40 +1,41 @@
 import bigben/fake_clock
-import birl
-import birl/duration
+import gleam/time/calendar
+import gleam/time/duration
+import gleam/time/timestamp
 import gleeunit/should
 
 pub fn fake_clock_set_now_test() {
-  let assert Ok(now) = birl.parse("2024-04-13T01:33:46.382Z")
+  let assert Ok(now) = timestamp.parse_rfc3339("2024-04-13T01:33:46.382Z")
   let clock = fake_clock.new_at(now)
 
   fake_clock.now(clock)
-  |> birl.to_iso8601
-  |> should.equal(birl.to_iso8601(now))
+  |> timestamp.to_rfc3339(calendar.utc_offset)
+  |> should.equal(timestamp.to_rfc3339(now, calendar.utc_offset))
 
-  let assert Ok(new_now) = birl.parse("2025-04-13T01:33:46.382Z")
+  let assert Ok(new_now) = timestamp.parse_rfc3339("2025-04-13T01:33:46.382Z")
   fake_clock.set_now(clock, new_now)
 
   fake_clock.now(clock)
-  |> birl.to_iso8601
-  |> should.equal(birl.to_iso8601(new_now))
+  |> timestamp.to_rfc3339(calendar.utc_offset)
+  |> should.equal(timestamp.to_rfc3339(new_now, calendar.utc_offset))
 }
 
 pub fn fake_clock_advance_test() {
-  let assert Ok(now) = birl.parse("2024-04-13T01:33:46.382Z")
+  let assert Ok(now) = timestamp.parse_rfc3339("2024-04-13T01:33:46.382Z")
   let clock = fake_clock.new_at(now)
 
-  fake_clock.advance(clock, duration.days(3))
+  fake_clock.advance(clock, duration.hours(3 * 24))
   fake_clock.now(clock)
-  |> birl.to_iso8601
+  |> timestamp.to_rfc3339(calendar.utc_offset)
   |> should.equal("2024-04-16T01:33:46.382Z")
 
-  fake_clock.advance(clock, duration.weeks(6))
+  fake_clock.advance(clock, duration.hours(6 * 7 * 24))
   fake_clock.now(clock)
-  |> birl.to_iso8601
+  |> timestamp.to_rfc3339(calendar.utc_offset)
   |> should.equal("2024-05-28T01:33:46.382Z")
 
-  fake_clock.advance(clock, duration.months(9))
+  fake_clock.advance(clock, duration.hours(9 * 30 * 24))
   fake_clock.now(clock)
-  |> birl.to_iso8601
+  |> timestamp.to_rfc3339(calendar.utc_offset)
   |> should.equal("2025-02-22T01:33:46.382Z")
 }