Other durations
About a 5 hours 40 minutes alarm
5 hours 40 minutes is about 3.8 sleep cycles of 90 minutes. If you want to wake at the end of a cycle, the alarms below at 4 hours 30 minutes and 6 hours are the closest cycle boundaries.
If you fall asleep in the usual 14 minutes, 5 hours 40 minutes gives about 5 hours 26 minutes of sleep, roughly 3.6 sleep cycles of 90 minutes. Waking at the end of a cycle feels better than waking in the middle of one: the closest cycle-friendly alarms are 4 hours 45 minutes and 6 hours 15 minutes from now (each allows about 15 minutes to drift off).
5 hours 40 minutes is 340 minutes, or 20,400 seconds. In hours and minutes that is 5 h 40 min. The alarm time updates live above, so the number you see is the actual clock time it will ring if you press the button now.
The alarm is created as a one-time alarm at the exact clock time, so you can see it in the list above, rename it, or switch the sound. Keep this tab open with the volume up; on desktop it rings from a background tab, on a phone keep the page in the foreground and the screen stays on automatically.
Prefer a countdown?
If you want to watch the time tick down rather than set a clock time, use the timer instead. Both ring with the same sounds.