Recommended egg withdrawl is 10-14 days. In honesty, many people ignore that and continue to use the eggs. Do what you are comfortable with.
I worm 30 to 35 birds every 3 months, I can do that in a little less than an hour. Gets easier with practice. So it's doable if you divide up the groups. Do it by coop, or by breed. Just get all your supplies ready the night before so it's all ready to go. I carry the wormer, a small dish/bowl (I find it easier to draw doses from that than from the bottle), a couple of oral syringes (in case something happens to one, you have a spare), a large towel for wrapping birds that fight being held, a small towel or rag (for wiping wormer off stuff, like your glasses

when someone shakes their head ), and a lantern or two since it will be dark, I use one in the coop and one in the run. And a scale if you need to get weights. After you've done this a few times it gets easier to estimate weights, I usually only have to weigh my adult birds once, and I weigh the young ones til they are full grown.