diff --git a/CHANGELOG.md b/CHANGELOG.md
index d6eea879d3..22cbc9ab5b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 ### Fixes
 
 - Resolve relative `SOURCEMAP_FILE` paths against the project root in the Xcode build script ([#5730](https://github.com/getsentry/sentry-react-native/pull/5730))
+- Fixes the issue with unit mismatch in `adjustTransactionDuration` ([#5740](https://github.com/getsentry/sentry-react-native/pull/5740))
 - Handle `inactive` state for spans ([#5742](https://github.com/getsentry/sentry-react-native/pull/5742))
 
 ### Dependencies
diff --git a/packages/core/src/js/tracing/onSpanEndUtils.ts b/packages/core/src/js/tracing/onSpanEndUtils.ts
index 758560ad06..45a12a04bb 100644
--- a/packages/core/src/js/tracing/onSpanEndUtils.ts
+++ b/packages/core/src/js/tracing/onSpanEndUtils.ts
@@ -39,8 +39,9 @@ export const adjustTransactionDuration = (client: Client, span: Span, maxDuratio
       return;
     }
 
-    const diff = endTimestamp - startTimestamp;
-    const isOutdatedTransaction = endTimestamp && (diff > maxDurationMs || diff < 0);
+    const diff = endTimestamp - startTimestamp; // a diff in *seconds*
+    const isOutdatedTransaction = diff > maxDurationMs / 1000 || diff < 0;
+
     if (isOutdatedTransaction) {
       span.setStatus({ code: SPAN_STATUS_ERROR, message: 'deadline_exceeded' });
       // TODO: check where was used, might be possible to delete
diff --git a/packages/core/src/js/tracing/span.ts b/packages/core/src/js/tracing/span.ts
index 90f2b401b8..7f0aa62622 100644
--- a/packages/core/src/js/tracing/span.ts
+++ b/packages/core/src/js/tracing/span.ts
@@ -30,18 +30,18 @@ export const defaultIdleOptions: {
    *
    * @default 1_000 (ms)
    */
-  finalTimeout: number;
+  idleTimeout: number;
 
   /**
    * The max. time an idle span may run.
    * If this time is exceeded, the idle span will finish no matter what.
    *
-   * @default 60_0000 (ms)
+   * @default 600_000 (ms)
    */
-  idleTimeout: number;
+  finalTimeout: number;
 } = {
   idleTimeout: 1_000,
-  finalTimeout: 60_0000,
+  finalTimeout: 600_000,
 };
 
 export const startIdleNavigationSpan = (
diff --git a/packages/core/test/tracing/adjustTransactionDuration.test.ts b/packages/core/test/tracing/adjustTransactionDuration.test.ts
new file mode 100644
index 0000000000..95cef9da80
--- /dev/null
+++ b/packages/core/test/tracing/adjustTransactionDuration.test.ts
@@ -0,0 +1,157 @@
+import { getClient, spanToJSON, startSpanManual } from '@sentry/core';
+import { adjustTransactionDuration } from '../../src/js/tracing/onSpanEndUtils';
+import { setupTestClient } from '../mocks/client';
+
+jest.mock('react-native', () => {
+  return {
+    AppState: {
+      isAvailable: true,
+      currentState: 'active',
+      addEventListener: jest.fn(() => ({ remove: jest.fn() })),
+    },
+    Platform: { OS: 'ios' },
+    NativeModules: {
+      RNSentry: {},
+    },
+  };
+});
+
+describe('adjustTransactionDuration', () => {
+  beforeEach(() => {
+    setupTestClient();
+  });
+
+  afterEach(() => {
+    jest.clearAllMocks();
+  });
+
+  it('marks span as deadline_exceeded when duration exceeds maxDurationMs', () => {
+    const client = getClient()!;
+    const span = startSpanManual({ name: 'Test Transaction', forceTransaction: true }, span => span);
+
+    const maxDurationMs = 60_000; // 60 seconds
+    adjustTransactionDuration(client, span, maxDurationMs);
+
+    // End the span 120 seconds after it started (exceeds 60s max)
+    const startTimestamp = spanToJSON(span).start_timestamp;
+    span.end(startTimestamp + 120);
+
+    expect(spanToJSON(span).status).toBe('deadline_exceeded');
+    expect(spanToJSON(span).data).toMatchObject({ maxTransactionDurationExceeded: 'true' });
+  });
+
+  it('does not mark span as deadline_exceeded when duration is within maxDurationMs', () => {
+    const client = getClient()!;
+    const span = startSpanManual({ name: 'Test Transaction', forceTransaction: true }, span => span);
+
+    const maxDurationMs = 60_000; // 60 seconds
+    adjustTransactionDuration(client, span, maxDurationMs);
+
+    // End the span 30 seconds after it started (within 60s max)
+    const startTimestamp = spanToJSON(span).start_timestamp;
+    span.end(startTimestamp + 30);
+
+    expect(spanToJSON(span).status).not.toBe('deadline_exceeded');
+    expect(spanToJSON(span).data).not.toMatchObject({ maxTransactionDurationExceeded: 'true' });
+  });
+
+  it('does not mark span as deadline_exceeded when duration equals maxDurationMs exactly', () => {
+    const client = getClient()!;
+    const span = startSpanManual({ name: 'Test Transaction', forceTransaction: true }, span => span);
+
+    const maxDurationMs = 60_000; // 60 seconds
+    adjustTransactionDuration(client, span, maxDurationMs);
+
+    // End the span exactly 60 seconds after it started
+    const startTimestamp = spanToJSON(span).start_timestamp;
+    span.end(startTimestamp + 60);
+
+    expect(spanToJSON(span).status).not.toBe('deadline_exceeded');
+    expect(spanToJSON(span).data).not.toMatchObject({ maxTransactionDurationExceeded: 'true' });
+  });
+
+  it('marks span as deadline_exceeded when duration is negative', () => {
+    const client = getClient()!;
+    const span = startSpanManual({ name: 'Test Transaction', forceTransaction: true }, span => span);
+
+    const maxDurationMs = 60_000;
+    adjustTransactionDuration(client, span, maxDurationMs);
+
+    // End the span before it started (negative duration)
+    const startTimestamp = spanToJSON(span).start_timestamp;
+    span.end(startTimestamp - 10);
+
+    expect(spanToJSON(span).status).toBe('deadline_exceeded');
+    expect(spanToJSON(span).data).toMatchObject({ maxTransactionDurationExceeded: 'true' });
+  });
+
+  it('correctly handles maxDurationMs in milliseconds not seconds', () => {
+    const client = getClient()!;
+    const span = startSpanManual({ name: 'Test Transaction', forceTransaction: true }, span => span);
+
+    // maxDurationMs = 600_000 ms = 600 seconds = 10 minutes
+    // A span lasting 601 seconds should exceed this limit
+    const maxDurationMs = 600_000;
+    adjustTransactionDuration(client, span, maxDurationMs);
+
+    const startTimestamp = spanToJSON(span).start_timestamp;
+    span.end(startTimestamp + 601);
+
+    expect(spanToJSON(span).status).toBe('deadline_exceeded');
+    expect(spanToJSON(span).data).toMatchObject({ maxTransactionDurationExceeded: 'true' });
+  });
+
+  it('does not mark span when duration is 599 seconds with 600_000ms max', () => {
+    const client = getClient()!;
+    const span = startSpanManual({ name: 'Test Transaction', forceTransaction: true }, span => span);
+
+    // maxDurationMs = 600_000 ms = 600 seconds
+    // A span lasting 599 seconds should NOT exceed this limit
+    const maxDurationMs = 600_000;
+    adjustTransactionDuration(client, span, maxDurationMs);
+
+    const startTimestamp = spanToJSON(span).start_timestamp;
+    span.end(startTimestamp + 599);
+
+    expect(spanToJSON(span).status).not.toBe('deadline_exceeded');
+    expect(spanToJSON(span).data).not.toMatchObject({ maxTransactionDurationExceeded: 'true' });
+  });
+
+  it('does not affect spans from other transactions', () => {
+    const client = getClient()!;
+    const trackedSpan = startSpanManual({ name: 'Tracked Transaction', forceTransaction: true }, span => span);
+    const otherSpan = startSpanManual({ name: 'Other Transaction', forceTransaction: true }, span => span);
+
+    const maxDurationMs = 60_000;
+    adjustTransactionDuration(client, trackedSpan, maxDurationMs);
+
+    // End the other span with a duration that exceeds the limit
+    const otherStartTimestamp = spanToJSON(otherSpan).start_timestamp;
+    otherSpan.end(otherStartTimestamp + 120);
+
+    // Other span should not be affected by adjustTransactionDuration
+    expect(spanToJSON(otherSpan).status).not.toBe('deadline_exceeded');
+
+    // End tracked span within limits
+    const trackedStartTimestamp = spanToJSON(trackedSpan).start_timestamp;
+    trackedSpan.end(trackedStartTimestamp + 30);
+
+    expect(spanToJSON(trackedSpan).status).not.toBe('deadline_exceeded');
+  });
+
+  it('handles very short maxDurationMs values', () => {
+    const client = getClient()!;
+    const span = startSpanManual({ name: 'Test Transaction', forceTransaction: true }, span => span);
+
+    // 100ms max duration
+    const maxDurationMs = 100;
+    adjustTransactionDuration(client, span, maxDurationMs);
+
+    // End after 1 second (1000ms > 100ms)
+    const startTimestamp = spanToJSON(span).start_timestamp;
+    span.end(startTimestamp + 1);
+
+    expect(spanToJSON(span).status).toBe('deadline_exceeded');
+    expect(spanToJSON(span).data).toMatchObject({ maxTransactionDurationExceeded: 'true' });
+  });
+});