When can I seal the picnic table I made from pressure treated lumber?
I used PT lumber for my basement outer walls.  I emailed PT lumber association (yes they have a website) and and asked how long I should wait before I slapped up the drywall. I was told that unless the lumber is in a very humid environment it will lose most of its moisture in 2-3 weeks.  I waited a month to be safe.  If the lumber is outside in warm weather shorter than 2-3 weeks.  They actually said I would be within code within a few days but the 2-3 weeks was just a safety precaution.  I just didn't want moisture hitting the drywall.

There is no arsenic in PT lumber now.   But if it is a picnic table a "sealer" that is good then it will be full of chemicals.  I would almost go with an oil based paint.