In Italy we are split between terroni (24th evening celebration and 25th lunch celebration) and polentoni (25th lunch and 26 lunch)

At the end happens often that families are mixed so you do all the 3. On top of that you have friends to meet and what’s best than another lunch/dinner?

In Germany, we usually have presents on the 24th in the evening, but the big family gatherings are often on the 25th (and 26th, as you’re typically part of multiple families).

Orthodox Christians celebrate on 7th of January

I’m in the US, and our family has always had the big get together on the 24th with extended family, then the morning of the 25th is a more personal thing where our individual families (and their children now) get together and exchange gifts.

So I don’t know if there’s any real generalization like that.