custom duration format google sheets 0 hours code example

Example: google sheets format number as duration formula

The accepted answer works for formatting a whole cell, but I wanted to
format only a part of the contents of a cell. I had tried using
TEXT(A2,"hh:mm:ss") but this is a date format and so does not work for
negative durations. However, TEXT(A2,"[hh]:mm:ss") does work for negative
durations.