If you're going on a night when they are scheduled for 8pm - with that reservation time you may not even be seated yet, but that's just based on my experience - I went during a moderately busy time and people were waiting for their tables for a little while. However, as long as you're checked in you should be able to go to the oberservation deck to see the fireworks; make sure they know you'll be out there in case your table becomes ready while you're viewing them.