You know, I never hunker down and grab a spot early anymore. If you don't mind NOT being by a railing overlooking the lagoon and just hang back a bit, you'll be ok. Not a stellar view, but nothing awful. I still think 7pm is enough time, though. Plan on getting to the restaurant 10 minutes early. You should allow an hour to an hour and 15 minutes...then when you're done, go out and grab a spot.
Is Biergarten buffet? That should make things move quicker...