as long as it is in your system I dont think it really matters...unless you are shooting suspension or taking an oral. I try to shoot my prop around the same time everyday, which is always pwo. Never before, I dont want it to interfere with lifting.
personally I prefer at least 2-4 hours before so some of it (and other test products I take) can get into the blood and have an effect for a better workout
Its just personal preference, no real rule on that one