Just considering that the step-in harnesses take .002 seconds to put on...step-click...and if he's that wild, well, I make mine stand on hind feet by putting my hand under their chests to put harnesses on, but yours is a pup so pick him up...and considering that they might get tangled up in, or even chew the harness and swallow pieces, I am wondering why/if you would really want to leave the harness on all day anyway.
For speed, you could instead keep the leash connected to at least 1 D-ring.
I have several harnesses for my dogs, but never leave them on full time, and never when I am not with them. Do try to get one that fits well, though!