Formatting time correctly

Hello,

I am trying to input data in elapsed time: 0, 15, 30, 45, 60. I would like the numbers that excel works with in seconds, but I would like them displayed as minutes and seconds, so 60 would be 1:00 and 75 would be 1:15. Is there a way to do this? I tried using the time formatting, but the time format wants explicit dates and times and not elapsed time like I want.

Thanks