I think it depends on the tea! With this one, it has absolutely zero bitterness or astringency that other black teas can get when oversteeped, so I just leave the leaves in the mug and keep topping up with more hot water when it gets low.
We have another black tea that my partner will do 1-2min on because it does start to get oversteeped for her. I’ll usually do 3min with that one because I like it a little stronger, but I can’t leave the leaves in indefinitely like with this jinjunmei.