Cool challenge and good introduction to the DateTimeDiff function.
I ended up using formulas where I took the difference between hours and then subtracted out [Days]*24. Got to the same place.
Had a difference in seconds though, but when I do the calculation by hand, my answer seems to be correct, not what is listed in the text output.
Interesting take though. Had to look up what a Modulo was when I compared my solution to the given solution.
Checked out some other solutions afterwards and really appreciate the diversity in approaches by others who have solved this. And the bonus is that I learned about the modulo function!