Butchering in the heat is helpful to have the offal and feathers (if you pluck) set far away from your work station as well as your hanging site (I use baling twine tied to a cross post and looped around the leg); in my experience the flies seem to flock to the discards. I butchered over 100 300lb+ hogs last May-June and found that bleeding and moving the discards far away helped a ton with the flies.
I typically do the birds by myself. I have a pot of water for the feet, a bucket with a bag set a couple feet away that I can toss stuff in and once the bag gets full I move it further away and start a new one.
I prefer to hand pluck and can dispatch, bleed out, scald, pluck, cut feet off, and gut a bird within 8-10 minutes. The birds then go into a 55 gallon lined can filled with ice water; as long as they’re submerged the flies don’t bother them.
I did 26 birds, dispatched 2 at a time, a few weeks ago and between waiting for more water to heat up, stopping to make lunch/help kids with something, and taking the neighbors dog home (she kept trying to get the hanging carcasses) it took me about 4 hours. Then the cutting and packaging took another 2-3 hours. In comparison, I helped my neighbors, new to the task, do 10 - I did 3 and helped them with theirs - and it took quite a while, but then again they didn’t pen the birds up the night before. I’m doing 25 tomorrow morning (going to dispatch 5 at once this time to try to speed things up) and then I’m done for a couple of months.
Once you do it more than a couple times or do several it’ll get easier and faster.