Normally, English native speakers use on and at with the festive holiday in the following manner
- We open our gifts on Christmas morning.
- We're going away at Christmas
The preposition on is used for dates, days of the week, and names of public holidays
e.g., Many florists make a profit on Valentine's day
But if a holiday covers a period of two or more days then the preposition at is used
- Children often hope for snow at Christmas
- We always stuff ourselves with chocolate at Easter
Recently, I discovered that in some parts of the US this is not always the case
While “on Christmas day” is hardly unusual, I would say that just “on Christmas” is the more frequently-heard expression, by a considerable margin. Might be a cultural thing, though (my experience is the American Northeast for the most part)
and in an old EL&U answer this phrase was submitted
We got together on Christmas for dinner and a gift exchange.
I also found supporting reference
*Note that in some varieties of English people say "on the weekend" and "on Christmas".
- Where do native English speakers omit Day/day and instead say on Christmas?
- Does on Christmas refer to 25th December, or is it also used to cover the entire holiday season?
This question is related, and inspired by the ELL question:
What is the difference between 'at Christmas' and 'on Christmas'?