We arrived about 5 minutes late when we went in December and were still able to find a table. Unless you haven't toured Launch Bay yet, or met any of the characters, there's not much to do at the party other than eating and drinking and there are no chairs. Will Movie Magic be shown that night prior to SWGS? If so, the stormtroopers will lead you out to the viewing area prior to that show so you can see it as well so I wouldn't be terribly late. Plus, honestly, the dessert tables got a little gross as the party went on, so I probably wouldn't push it past 15 minutes late.