This is fairly easy to do in Excel. Excel stores dates and time as numbers with each integer equal to one day. So 0.5 is 12 hours, for example. 1.5 would equal 36 hours.
What units is your 73.60 in? If it's hours, divide it by 24 to convert it to Excel days and set your cell's format to CUSTOM > dd:hh:mm
If it's in days already, just set the format.
EDIT: Oops, I should have tested first. This format does not work for greater than 24 hours. Some fancier formulas are, I think, needed.
[h]:mm will display hours (beyond 24) and minutes, but this is not what you asked.
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