Most magazines (Prima, Good Housekeeping, Good Food etc) will have a "timings" and recipes for Christmas Day in the December issue. (I don't have to sit at any particular time, so we just work away as it comes here - but we are only 3 people).
In advance and frozen:
Definitely at least make breadcrumbs for stuffing, if not the entire stuffing itself.
If you want soup for starter, that can be made now and frozen too.
I know lots of people have recipes and ideas for par-boiling roast potatoes and freezing, or having veg ready to cook in freezer.
Lots of stores have side things, like pigs in blankets etc, which can be frozen too.
The day before:
DH always make the stuffing. I defrost the breadcrumbs and he rings his mother to check the recipe, then cooks the sausage meat and makes the stuffing. That gets put in the fridge overnight.
I boil the neck/giblets etc, and wingtips, to make stock. I often then use that straight away to make the gravy, with a glug of wine included. Then I just have to reheat and add the turkey juices from roasting tray.
I peel all the potatoes and soak them in a pot on the cooker in cold water.
I peel and chop all the carrots, and put into cold water. (I tend to leave parsnips and butternut squash for the following day).
I peel and wash the Brussels sprouts, and cut the crosses into stalks, then put them in an airtight tub (no water).
I peel and slice the 2-3 onions I need, and put those in an airtight container (no water) for the couple of different things next day. I'll usually peel a couple of cloves of garlic and throw those into that tub on top, unchopped but 1 less small faffy job the next day).
I also make sure I have cheese grated for cauliflower cheese if we are having it, sometimes even making the cheese sauce. And I will prep the cauliflower (take off leaves, chop into florets, wash, and then leave soaking in water).
I will do a batch of whipped cream, for soup swirls, desert and dollop on top of coffee.
I slice lemon and lime (maybe an orange) for drinks needs, and if I think ahead enough, I will freeze them sliced reducing the need for ice for drinks. I'll also make sure I have all ice trays filled, and usually freeze 1 batch, turn out into a Tupperware tub, and freeze a 2nd, on Christmas Eve (or even more if needed) - with the rule that anyone who empties the ice trays refills to freeze again too.
Set the table, or at least get things organized to easily find and allow you to delegate that task on the morning if helpers are offering. Put a sticky note into serving dishes so you and helpers know what should be in each. Have things like desert dishes, cups etc relatively easy to get at when moving on from main course.
I also make sure I have run the dishwasher after all my prep, so that it's empty for the next day. And I try to run it again after breakfast and the first prep stuff is done in the morning, so it is empty to take starter/main dishes very easily and lets any helper to easily clear table straight to dishwasher.
That's all I can think of, right now. I know times that I do have loads of people in, I do a lot ahead of time. Lots of lists. Lots of timings. And lots of thinking ahead on how things should work, and how I can make sure that they will work (including WHO I can give SPECIFIC jobs to, and trust they'll get done).