How long can I let this go?

Oh, I forgot to mention that the only thing you need to keep in mind when you do it this way is that in rare cases, the plants might try to produce male flowers in the last act of trying to propagate themselves. Then you'll just have to harvest, but there probably won't be many buds left if you harvest them step by step.

Hi yeah, the tops look ready. So I often do it like this: I harvest the upper buds that are ready when at least 85% of the trichomes are milky. The lower ones that aren't quite ripe yet, I just leave them for a few more days until they're ripe too. That can take up to 2 weeks. The plant won't suffer as long as it still has time; what I mean is that eventually it will die because it's too old. But there are also many growers who just let the buds dry with the plant when it's done. I would do that if I were you.