How to format time in decimal format & calculate time
 

I used the CUSTOM function as [mm:ss], but it's not working as I thought that
it would. What I want is a user to type in the number of dictated minutes
they typed for a job; i.e: 2:30 (2 min. 30 sec) and have it stay in that
format as decimal after entered. However, I'm getting results of 12:00 for
that example when using the format stated above? I also want to add these
dictated minutes and have the result calculated in H:MM:SS. HELP? I've tried
everything!