"Advanced" User online time threshold display

[MrPrise]

Not a big deal, I think I can code this but I would like to have this in the official release, not as my hack.
The problem is that, when I change the user online time threshold to 24 hours (1440 minutes) it displays as minutes instead a more human readable format. If the minutes is more than a hour it should shows the number of hours (only or with minutes), if the minutes is more than 24 hours it should shows the number of days.
If the admin can set a format string for that (like in the time format) that would be the best solution.

Thank you and Merry Christmas to all of you! :-)