Momo1991: Input is always welcome - should the deadline be sooner??
Take a look at
last year's event - leaving more time between deadlines (there are more than one) will work better for all parties.
Keep in mind that if previous years are anything to go by, GOG's big Winter Sale will start around Dec 12, so the first deadline (entries with wishlists) could be on or around that date. You could then use the weekend to assign people to each other and send out the PMs. If the next deadline is set around Dec 20-21, peeps will have around a week to stuff their bag of gifts and send it to you. This would give you a few days to sort out potential glitches before Xmas Day.
I'd also like to point out that I'm not in favour of sending gift codes to your email from the checkout page, as GOG discloses the email address that the gifter uses on GOG in the email the recipient gets.
nmillar allowed PMs for this part too, that's how I did it in past years, and it's something I'd like to be able to do for this year's event.
EDIT: typo