I know that it may be irrelevant, it's a feature that seems rather unimportant, but somehow Playnite does it in a universal way. It doesn't matter which emulator you are running, it calculates the time when you start and exit a specific game. I admit that it's not the most accurate method but it works good enough. Honestly, it's one of the few things that I really miss on launchbox and I don't see any interest in it, which makes me sad. Anyway, let's hope that someday it will be implemented in some way.