Either way...doesn't matter
The weight of the bike (or lack thereof) won't affect the pressure. As Jack says, check and adjust when cold.
I would think that bike needs to be on the ground.
The tire IMO is just like a Balloon, the more pressure you put on it, builds up the inside pressure ......untill POOF !
Agree w/Jack - bike grounded, cold & use decent gage. I ended up getting HD's dial gage to fit into the tight space under back tire/swingarm/bags.