Question 1

What format should I enter the start hour in?

Accepted Answer

Use 24-hour format (also called military time): 0 = midnight, 1–11 = 1 AM to 11 AM, 12 = noon, 13–23 = 1 PM to 11 PM. So 3 PM is entered as 15, and 9 PM is entered as 21. The result is shown in both 12-hour (AM/PM) and 24-hour formats.

Question 2

Does the calculator handle midnight crossovers?

Accepted Answer

Yes. If you add time past midnight (e.g. 11:00 PM + 2 hours = 1:00 AM) or subtract past midnight (e.g. 1:00 AM − 90 minutes = 11:30 PM the previous day), the calculator correctly rolls over and tells you which day the result falls on.

Question 3

What are some practical uses for this calculator?

Accepted Answer

Medication timing (take again in 4 hours), cooking (roast needs 2h 45m, put it in at what time?), meeting end times, parking meter expiry, shift end time, DNS / cache TTL expiry, and deadline countdowns are all common uses.

Question 4

Can I calculate what time it was X minutes ago?

Accepted Answer

Yes — switch the operation to 'Subtract time (backward)' and enter your current time as the start. The result will show what time it was that many minutes in the past, including rolling back past midnight if necessary.