If you market to businesses, you are pretty much leaving a flyer for the secretary in charge of putting together office parties. Many businesses have a policy against posting ads on the break room bulletin board (a number of places I worked at had such policies) so the majority of the employees wouldn't know about your flyer that you left with the front desk person.
An angle to achieve that might be to offer a discount to "The Employees of XYZ Company". Some companies market those kinds of discounts as a benefit to their employees and would post that info on the breakroom bulletin board or company newsletter. I would suggest calling to see what their posting policy is w/ or w/o a discount. I've worked at companies where I got a discount at Pizza Hut, pharmacies, and other places just because I worked at my company.
This would cost a little more, but you might look into direct mail marketing. And don't just buy some random mailing list ... work with a direct mail marketer who can narrow down the mailing list to the demographics you're looking for. You'll find it's chepaer than you think.
Now is the time. It's only 6 weeks away. We all complain when Christmas stuff is out before Thanksgiving, but a lot of folks I know are thinking about and buying Christmas way before Thanksgiving anyway.
And on Feb 15th, this site will be buried in posts that are laughing about all of the people who waited until Feb 13th to try to order cookie bouquets!
So get them to think about it early and order early.
I would encourage "pay at time of order" as a benefit to the customer. You know they will be busy on this very special day and when the order is paid in advance, ti's one less thing the customer has to think about. Just breeze in and pick it up!