I've use screened bottom boards for 10+ years, but I always have kept a tray underneath filled with agricultural lime. The bees push debris, beetles, larvae down through the screen and it falls into the tray, allowing me to see what has been bothering them. I can also see some of the pollen that they're bringing in as it falls through. I was working crazy hours and could not alwzys inspect them that's the way I should. this year I'm changing some out for solid boards just to see what differences I noticed. I don't think it matters when, or if you switch them out. I'm sure others will chime in on their preference.
i prefer solid bottoms. Makes treating for mites easier and in my opinion bees will cap honey sooner as they can better control humidity in the hive.
I've use screened bottom boards for 10+ years, but I always have kept a tray underneath filled with agricultural lime. The bees push debris, beetles, larvae down through the screen and it falls into the tray, allowing me to see what has been bothering them. I can also see some of the pollen that they're bringing in as it falls through. I was working crazy hours and could not alwzys inspect them that's the way I should. this year I'm changing some out for solid boards just to see what differences I noticed. I don't think it matters when, or if you switch them out. I'm sure others will chime in on their preference.