I disagree.
Using the “h” is an anglicism. Sure, everyone will understand it, but it is English – not Finnish. The formal way of expressing time is:
7 t 15 min (= 7 h 15 min)
Source: Kielikello, a magazine focusing on formal/proper Finnish. They have an awesome collection of online articles available, in Finnish.
Edit:
Since Discourse is being translated to Finnish, the target should always be proper/formal Finnish, IMHO. Anyone can switch their locale to English if that is the personal preference.