Unit to display for 00:00 minute:second format [duplicate]

This question already has an answer here:

What would be a way of making clear the distinction between 00:00 min:sec format and 00:00 hour:min format? Due to spacing constraints (driven by specific client specs regarding font sizes; this is an embedded HMI), I can neither use full format (00:00:00) nor is there space for a full min:sec / hour:min pseudo-unit.

I'm thinking of using "h" for the hour:min entries and "min" for the "min:sec" entries, but this not really intuitive.