Tell me what was the most difficult. It doesn't have to be! I have been raising birds for food since 1983 off and on.
I take notes each time about what would have made it faster, easier and more humane.
Since I hatch and raise so many, I have such a large supply of roosters I may only do "meaties" 2 times a year now if that.
I wouldn't think the water temp should change. When you do the pull test to see if the wing or tail feathers pull easily they are ready.
the farthest wingtips at the joint will tell you the most, as well as the tail feathers.
The trick is short frequent dunks (15-20 seconds) and swishes, check, dunk, swish, repeat. When the tail feathers pull easily dunk in ice water.
I HATE plucking since I have stiff hands from arthritis, so I have tried very hard to make it easy for me.
The plucking was hard. I wore out my hands pulling stiff quills and tore skin over the fatty places. I thought it was because the magic temperature (150 degrees) didn't function the same at 7,000 feet (it happens for baking/cooking) but maybe it was because I dunked two at a time and the second cooled to much by the time I'd got through plucking the first?
I did "test" by making sure the wing feathers slipped easily. But did not dunk in ice water.
I agree on the take notes and adjust approach. So trying at the end of this year to figure out what to do to make next year better.
Appreciate any advice/thoughts!