Other durations
About a 2 hours 40 minutes alarm
2 hours 40 minutes is roughly one full sleep cycle, the length that tends to leave you feeling refreshed rather than groggy. It works well as a recovery nap after a short night.
If you fall asleep in the usual 14 minutes, 2 hours 40 minutes gives about 2 hours 26 minutes of sleep, roughly 1.6 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 1 hour 45 minutes and 3 hours 15 minutes from now (each allows about 15 minutes to drift off).
2 hours 40 minutes is 160 minutes, or 9,600 seconds. In hours and minutes that is 2 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.