View the original community article here
Last tested: June 15, 2020
The general logic here is, if the time diff is negative, then build own results using diff_minutes/diff_seconds, otherwise; do the calculation.
if(${history.created_time}<${history.completed_time},concat("-",ceiling(diff_minutes(${history.created_time},${history.completed_time})/60), ":", abs(mod(diff_seconds(${history.created_time},${history.completed_time}),60))),to_string(${history.completed_time}))
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