docs: clarify fake timer usage with user-event

docs/guides-using-fake-timers.mdx

@@ -10,11 +10,8 @@ flaky.
 
 To solve these problems, or if you need to rely on specific timestamps in your
 code, most testing frameworks offer the option to replace the real timers in
-your tests with fake ones. This should be used sporadically and not on a regular
-basis since using it contains some overhead.
-
-When using fake timers in your tests, all of the code inside your test uses fake
-timers.
+your tests with fake ones. This has a side effect - when using fake timers in
+your tests, _all_ of the code inside your test uses fake timers.
 
 The common pattern to setup fake timers is usually within the `beforeEach`, for
 example:
@@ -26,12 +23,10 @@ beforeEach(() => {
 })
 ```
 
-When using fake timers, you need to remember to restore the timers after your
-test runs.
-
-The main reason to do that is to prevent 3rd party libraries running after your
-test finishes (e.g cleanup functions), from being coupled to your fake timers
-and use real timers instead.
+Since fake timers are mocking native timer functions, it is necessary to restore
+the timers after your test runs, just like regular mocks. This prevents fake
+timers leaking into other test cases and cleanup functions, where real timers
+are expected.
 
 For that you usually call `useRealTimers` in `afterEach`.
 
@@ -51,3 +46,11 @@ afterEach(() => {
   jest.useRealTimers()
 })
 ```
+
+:::note
+
+Combining fake timers with `user-event` may cause test timeouts. Refer to
+[`advanceTimers`](user-event/options.mdx#advancetimers) option to prevent this
+issue.
+
+:::

docs/user-event/options.mdx

@@ -8,8 +8,21 @@ can be applied per [`setup()`](setup.mdx).
 
 ### advanceTimers
 
-If you are using fake timers, you need to advance your timers when we internally
-[delay](#delay) subsequent code.
+`user-event` adds a [delay](#delay) between some subsequent inputs. When using
+[fake timers](/guides-using-fake-timers.mdx) it is necessary to set this option
+to your test runner's time advancement function. For example:
+
+```js
+const user = userEvent.setup({advanceTimers: jest.advanceTimersByTime})
+```
+
+:::caution
+
+You may find suggestions to set `delay: null` to prevent test timeouts when
+using fake timers. That is not recommended, as it may cause unexpected
+behaviour. Starting from v14.1, we suggest using `advanceTimers` option instead.
+
+:::
 
 ```ts
 (delay: number) => Promise<void> | void