I give you my expression to calcutate an average time on several days.
the [time] column has a duration type.
This can be used to do any operations on the time.
time(
concatenate(
floor(totalseconds(sum(timeTable[time])) /count(timeTable[time]) /3600),
":",
floor(mod(totalseconds(sum(timeTable[time])) /count(timeTable[time]) ,3600) /60),
":",
round(mod(totalseconds(sum(timeTable[time])) /count(timeTable[time]) ,60))
)
)