How Could I SUM the Time Format 00:00 (hr:min) In Numbers?

I have downloaded from external app a driving duration report. It gives me the values only in for example 01:12
Which would be 1 hour and 12 min. I would like to SUM all the columns to get the monthly driving report in hours, minutes, sec.
When I choose in Numbers under “Cells” → “Data Format” → “Duration”, it reads it as minutes and seconds.
I tried to add format as 01:12:00 ( which would be 1 hour 12 minutes and zero sec ) it reads automatically as a date, but after switching to a custom units hr min sec nothing happens, it doesn’t change.
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Joze, Germany