Outdoors I spray BT right up till almost the end. I try not to spray them the final 2 weeks. If for some reason they were sprayed an I want to chop them and it hasn’t rained on them since I sprayed them with BT I’ll wash the chopped plants with water and then hang to dry.
I’ve never noticed this having an adverse effect on the buds? It’s possible it does but the threat posed by caterpillars to your buds is highest the last few weeks of your grow. It’s like the caterpillars love frosty buds (more like the buds are the biggest they get at the end too)? So I’ve always kept spraying BT to the end.
One of the worst feelings in the world is to spend 6 plus months raising plants to achieve your dream harvest only to see hundreds of caterpillars dropping out of your newly harvested bud. They can ruin it all in a matter of days.