[aristeides]

I assume they've got to go into recess before the new Congress starts in January, if not before then. So then will be the opportunity to make recess appointments.

[mrsmith]

I don't think "they've got to" though they traditionally take a long Christmas recess.

The significant point seems to be whether the senate is available to perform it's "advise and consent" function.
That depends to some (undetermined as far as I can find) extent on the length of the recess. The shortest recess anyone seems to have argued justified recess appointments is three days.

There are a lot of rules and arcana on this.
A pdf file on the web is "Recess Appointments of Federal Judges" by the CRS on September 5, 2001. Sorry I can't give a link but it should be easy to find using the title.