Jacob
What goes around comes around.
No it's easier if you cut to length first!Well, this is a hobby (the woodworking). There's a small minority who would probably like to work entirely by hand, but information from folks like Jacob is going to leave them thinking it's harder than it is. .......
Don't worry D_W you are not the first to make this mistake, but the first I've heard of trying to do it by hand!
Amongst other things you get better "yield" if you plane last. This is because you have to remove more stuff from a long piece to remove bends or twists, than you would if you had cut the same piece into shorter lengths. Also if you do it too soon it may have moved and need planing again. This is common with bought PAR - say 25mm sawn ends up PAR at 18mm, then you get it home and have to take more off to take out the twists.