Time Formats

I'm building an excel spreadsheet for my movie collection. I've gotten to the point where the total runtime of my entire collection, right now, stands at about 43 days (over 1,030 hours). I can have excel format the cell to indicate dd:hh:mm:ss, but if mm is minutes, what can I use for months? Obviously, formatting the cell as mm:dd:hh:mm:ss messes it all up, because it's inputting the minutes twice.

If this is not an option, what would be my best course of action to get a precise total runtime, down to the second?

Why bother with months? Months are not precise; months contain a variable number of days.

Yes. use this Custom Format:

d, hh:mm:ss