The store typically takes at most 5 working days for processing submissions but they have advised that due to traditionally larger volumes at this time of year things may take longer than usual*.
The announcement was made in the Dev Center forums but you may have missed it. (Don't feel bad, I don't monitor the forums too carefully either.)
If you want the app certified by Thanksgiving, you should submit it by Wednesday, November 20th.
If you want the app certified by Christmas, you should submit it by Monday, December 16th.
If you want the app certified by New Years, you should submit it by Friday, December 20th.
Of course submitting early won't hurt and meeting these dates still doesn't guarantee it will pass certification if it doesn't meet all the requirements.
* For reference I submitted an app on Sunday just gone and it was ready this morning. Taking approx. 4 days.