Is there a certain time when he's supposed to be there, or is it random? Can I visit the cottage several times, even if I don't have gifts to collect?

I believe he'll show up one certain day, and you can go any time that day.

I think that's how it worked last year anyway.

ok, thank you :) I wonder if there's a board where I can get an alert, or something when it happens

Yeah. is right. It was either December 24 or 25 last year. I can't remember, but he was there all day so no matter what time you went by you got the achievement. Just be sure to go to the cottage every day and you shouldn't miss it.

cool. thanks :)