Try a calc set as number:
"Time under water " & Minute (TimeField) & ":" & Seconds ( TimeField)
Almost worked however when the seconds are 00 only 0 is shown for seconds. Would like seconds to be 00.
Layout text with the time field included as a merge field might be simpler, but:
Right ( "0" & Seconds ( TimeField) ; 2 )
will include a leading zero.