I generally need to hit the ground running after TPACs, so I do whatever I can to help me sleep. I'm usually the first into the washroom after the fasten seat belts light goes off and into my "lounge pants".
In all the F Class longhaul flights I've taken it's a race to the washroom to see who can change first - some even changing before takeoff. That seems too extreme for me. I mean, what happens if there's an unexpected deplaning. PJs are the norm in First Class but don't look too good if you're asked to return to the terminal and wait on maintenance.