Well, if it were me, I would look at the dates historically for the past couple of years and you can probably get a good idea of when the parties will be. The dates in December are a lot easier to guess than November, typically Tuesdays, Thursdays, Fridays, and Sundays, until the weekend before Christmas. If you are booking room only, you could make two reservations for different dates and then cancel one when it doesn't meet your requirements, as you can get your deposit refunded easily up until 6 days prior to check in.