Generally when I have checked fork oil/rebuild forks, I tend to do it with the forks off the bike. I have seen people replace springs/shims in their forks with the forks on, but their not replacing fluids, or checking anything with the fluids.

If your going to do it with the forks on the bike, I would probably think you want to suspend the bike from the triple tree so you have no weight on the forks.
_________________
Charles Gallant