I usually send them out in mid-December, a couple of weeks before Christmas. Early December for those that go out of the US. No particular time though, just try to make sure they are received before the holiday.
And do you buy "Holiday" stamps or just whatever ? I've done different things in different years. Looked at the holiday ones this year & ended up just buying ones with star spangled banner on, looking like fireworks .
I just use regular stamps, the ones we've been getting from the post office have birds on them, I always choose something related to nature if I can. The global stamps I'm using for out of country just happened to be Christmas wreaths, so I'm okay with that, they look nice.
During the first week in December for over seas ones.. and in Australia 2 weeks before Christmas not that I have a lot to send any more..
just a few.. but it is so nice to receive snail mail or posted Christmas cards.. not many people do it now as they are on the net.. I love Christmas too..