Stocking presents for us could be opened as soon as we woke, and as they always involved a satsuma, a small pkt of nuts and some chocolate, we could scoff the lot if we wished. But we had to stay in our rooms until Mum came in to get us downstairs for breakfast.
Other presents opened starting very late morning ( with a snack, coffee, chocolates etc) basically after Mum had got the kitchen stuff on the go and could sit down with a coffee and the only sherry she was allowed all day :(
and Dad got started on the first of very many whiskys, but that's another thread :(
and we all took it in turns to open presents from each other.
but if there were family or friends coming round later we waited to open any presents from them under the tree, until they arrived.
Always spread over the day, not a "grab and rip" open everything in the first few mins.
Dad , (born 1931) was very controlling and abusive, but curiously not about Christmas especially - maybe because he just got totally pissed?
Or maybe I dont remember Christmas as especially tense, because tbh it was so crap all the time around him anyway.
or ( very likely) my Mum made a huge effort to keep him sweet so he didn't spoil it for us children.
DH the same in his family, without the control or abuse of course, and we do the same now with our children and friends.
But, if we are not seeing people on The Day, presents can be opened in advance, when we meet up. or the following week if we schedule a Christmas meet up - its meant to be fun, after all!