You can choose how many times the alarm and notifications repeat after the timer ends in Settings.
Android: Alarm Count
In Settings, tap "Alarm Count".
Choose "1x" to "10x", or "Repeat Forever". A checkmark marks the selected option.
With "Repeat Forever", the alarm repeats after the timer ends until you tap "Done". Notifications repeat when the app is closed. This is separate from "Repeat Count", which repeats the timer itself.