For alarms and clock times, my guess is data validation. The app could correct or block invalid time entries (e.g., accidentally hitting 2500), or it could restrict the entry set.
It also means the number will be in the correct format. your example, 930, could mean many things (930 seconds? 9:30am or 9:30 pm?)
But an alarm clock sets a relative point in time that happens every day. Putting "3 days" into a calendar is fine, but for an alarm clock it makes no sense.
It also means the number will be in the correct format. your example, 930, could mean many things (930 seconds? 9:30am or 9:30 pm?)