Kind of surprised this wasn't already out there but here is a converter for a duration in decimal form to something else. You might end up with a decimal duration when doing math on two date/time columns like:
([Date1] - [Date2]) * 1.
Conversion Measure =
VAR __Value = SUM([Decimal Days])
VAR __Days = TRUNC(__Value)
VAR __Hours = TRUNC ( (__Value - __Days) * 24 )
VAR __Minutes = TRUNC ( (__Value - __Days - __Hours / 24) * 24*60 )
VAR __Seconds = TRUNC ( (__Value - __Days - __Hours / 24 - __Minutes/24/60) * 24*60*60 )
RETURN
__Days&":"&__Hours&":"&__Minutes&":"&__Seconds
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Thank you. This is great.