I suggest splitting that time field into 3 separate columns for hours, mins and seconds (do this by expand value operation on the ":")
then creating a new field that is the summation of the time in just seconds where it is:

[Total Time (s)] = [Seconds] + 60*[Minutes] + 3600*[Hours]

The total time in this case would be an integer and not a date/time.

Then for average session duration it would just be [Total Time (s)]/[Sessions]
To get minutes just divide that by 60 and for hours by 3600.


If you want to do it in just one single field the formula* is a bit long but would look like:

[Total Time (s)] =

numvalue(right([Session Duration],2))
+
60*numvalue(left(right([Session Duration],5),2))
+
3600*numvalue(left([Session Duration],(len(Session Duration)-6)))

Then divide that by [Sessions] and 60 for mins and 3600 for hours.

Most likely your session durations would be in the seconds or minutes at most, not hours.

*Just an addendum for the second formula, if you use left or right functions you have to make sure your time/session duration field is always defaulted to text. The numvalue() will change the individual subtext into a numerical format for your output.

Thanks for the suggestion.

Once I get to seconds, is there a formula that can convert this back to the minutes:seconds format?

For example:
Rather than 80 seconds showing 1.34 minutes (80/60), having it output 1:20 (1 minute plus the 20 seconds as a remainder)?

This should give a text output format in terms of minutes:seconds, just create a new field where duration is the time duration in seconds of the previous formula.

IF(
[Duration]>60, intfloor([Duration]/60)+":"+([Duration] - (intfloor([Duration]/60))*60),
[Duration]
)