Duration fields are awesomely useful. However, if one wants to simply transfer the displayed duration (e.g. 1:45) to another field via a formula, Airtable passes along the stored value in seconds. Converting that back into a duration-like display is doable, but a little tricky, as I found out in this recent discussion:
I tried the TIMESTR() function, but that just gave an error, so I ended up writing my own seconds-to-duration formula.
My suggestion: expand the TIMESTR() function’s capabilities to also convert durations into strings. I suppose a new function named something like DURSTR() might also work, but because durations are all about time, wrapping that conversion into TIMESTR() feels like it makes more sense.