how early should you arrive at the christmas service to get a seat

it Depends on the service. Thursday 6:45 and Friday 3:30, 5:45, and 7:30 Sat. 3:00, 4:45 and 6:30 sat. services will probably be fuller but 15 min most likely be fine 30 min if you want to mingle:) merry Christmas

I would be about 20-30 mins early...

1 hour