Technically, "forever", since there will be people who never port their code. If you're depending on one of those holdouts, it's time to find a new dependency,

Technically, "forever", since there will be people who never port their code. If you're depending on one of those holdouts, it's time to find a new dependency, because if they haven't ported by now they won't and that's your problem because... in practical terms, the transition is about to be over, since now the Linux distros are all-in on converting to Python 3 for their current or next releases and that will forcibly move the unported libraries in the bin of obsolescence.