You should check with your employer the rules on your vacation pay.
I can roll unused vacation pay to the next years up to a maximum of 400 accumulated hours I think, then I'd have to cash some in. I cash some in anyway on a paycheck if I didn't work enough hours, that way I know I can pay my bills.
I suppose a person can get an exception to take off in December if they have someone to cover for them but it is frowned on & normally December we don't have enough seasonal workers to cover offices as it is. UPS & FedEx drivers can't take December vacation either.