I have generally had to work on Xmas Eve morning so we've all gone to town, and had a nice lunch there once I've escaped...so we only start prep in the early afternoon. Music on, DH and I working together, DD partially helping in younger years (now we hope she disappears to her room for her own music to avoid a row...teenage years).
Prep involves peeling potatoes and putting to soak in water in a pot, peeling and chopping carrots to soak in water in an airtight tub, peeling and chopping parsnips to put in airtight tub (ditto onions and garlic), peeling and putting the cross in the stalk of sprouts, cooking sausage meat (and the annual phonecall from DH to DMIL to remember how to do that) and making stuffing, chopping herbs and mixing into softened butter, some years brining the turkey, etc. I usually also make stock with the turkey giblets and the carrot and onion peelings.
Working together, that takes about an hour/90 minutes.
On the day, it takes a few minutes (maybe 20?) to prepare the bird (stuffing in bum, herby butter under skin, streaky rashers laid over the top, foil tent over the roasting tin), which we do when we get in from mass and a couple of extended family visits. I also throw a tray of M&S party nibbles into the oven at the same time, while we light the fire, open wine, find a nice drink for DD, light candles etc.
The rest of dinner is prepared in fits and starts in between opening presents and refilling wine. No more than 5-10 minutes in the kitchen at a time, in between long periods in the sitting room. Baste turkey a few times initially, turn on potatoes to steam/boil for 15 minutes just before turkey comes out, put foil tent back over turkey on the carving dish and cover with 2 towels (to keep heat in while it rests for another hour) and at the same time toss potatoes in fat (olive oil, duck or goose fat, depending on preference) to throw into the oven to roast, turn on carrots/parsnips to steam for 15 minutes. Next visit is to toss carrots, parsnips, onion, garlic in olive oil, juice of 1 clementine and some thyme, salt/pepper before throwing them into the oven for 45 minutes.
Then it gets a little hectic with about 30 minutes to go - making gravy (which could be done while waiting for root veg to steam or in the final stretch), steaming sprouts, doing any other veg we want (maybe wilted spinach or baby peas), putting plates/serving dishes in to warm, setting the table (which can easily be done earlier - but we use it for nice breakfast and it works to do this way for us).
Our party food nibbles are the starter, supplemented with nice crisps or hummus and breadsticks if necessary. But you can make soup ahead of time to just gently reheat (if a nice low heat, don't need to constantly stir, just when you are out doing other jobs anyway).
We do have a pudding, but generally a couple of hours after main course. But if you want it straight away, just put it on to steam as you are in that final 30 minutes and a ring gets freed up.
I know I have seen lots of people talk about doing they steaming and tossing in fat of potatoes the day before or even a while before and freezing them so they just go straight into the oven. And the same with red cabbage. I am sure you could do the steaming and tossing into the seasonings of the roasted roots the day before also (the onion and garlic go in cold), and either or both onion and garlic could be left out if necessary. I have made the gravy the day before also on occasion and just reheated it and added the turkey juices to the pot (my gravy uses bisto powder rather than flour though, so it is pretty quick to make once you have 5 minutes to stir initially).
I know DM used to always cook the ham the day before (boil and bake it) and reheat that in the steamer on Xmas Day, but turkey would be roasted on the day. Then again, turkey sliced up and reheated in its gravy is a great dinner another night, so that could well also work for Christmas Day.
I know we only do it for 3, but I grew up in a large family so catering for crowds is not that different. Instead of 1 hour prep on 24th, it would be 1.5-2 hours, and needing larger pots and tubs to put things into.
I try and already have breadcrumbs made (from ends of loaves we wouldn't otherwise eat) and frozen to just pull the bag from the freezer. And I tend to skin onions early on in the prepping, so I can ignore the slow frying of 1 diced onion for the stuffing while I do something else.
And we used to get DD involved by finding the vegetables in the fridge/cupboard, sweeping the floor, finding the best music station on the radio, getting out the big pot for the potatoes, count if we had enough potatoes/carrots/sprouts, counting enough nice napkins in a pile for everyone ready to set the table, ....little jobs she was able to do, not terribly getting in our way and making her part of the effort. As she got older, she could do some peeling and chopping as well - and then she hit teenage years where she is perfectly capable but not really interested so it's back to me and DH at the moment.