A Realistic Timeline for Family Christmas Cards
Every year the same thing happens. The cards get designed in the first week of December, the printer queue is three days long, and half of them arrive after the holiday. The printing was never the slow part. The photograph was.
Six to eight weeks out
Decide the format — folded card, flat card, or a printed photo — and how many you need. Count the list properly, once. Running out and reordering ten is more expensive than ordering ten extra.
Book the photograph now if you are using a photographer. If you are taking it yourself, this is the window to try a few setups, because the one you plan in your head rarely works on the first attempt in a room full of children.

Four to five weeks out
Take the photograph. Whatever the plan was, take more than one and take them in daylight. Diffused light through a window beats a flash every time, and the difference shows up immediately in print.
Choose the image and write the message. Short works better. A single line plus names is enough, and it is far easier to lay out than a paragraph.
Three weeks out
Print. If you are printing at home, do one test card on the actual card stock first. If you are using a print service, this is still early enough to catch a cropping problem and reorder.
Address the envelopes during this week, not later. This is the task people underestimate, and it is the one that slips.
Two weeks out
Assemble and post. If you want cards to arrive before the holiday, this is the week to be in the post box, especially for anything going overseas.
What to do differently next year
Keep the address list in one file and update it when people move, rather than rebuilding it every November. Note the paper you used and whether you liked it. And if the photograph is always the bottleneck, take it in October when the light is still decent and nobody is rushing.
One practical note on returns: put your own address on the back. Cards come back undelivered more often than people expect, and an addressed card is far more likely to find its way.