If by 'see' you mean go into EPCOT, find a decent spot, and watch it, I would say you need an ADR between 6 and no later than 6:30, and maybe even earlier than 6 (those good spots can fill up early, depending on what time of year you are going) If you mean walk outside FF and see it from the BW or the lake area, or if you don't care much about getting a good spot around EPCOT, then 7 is probably safe to get you out of FF in time to see it.