I know I'm not part of the whole thing but I would give bigger window than that due the time zone differences and all that. Something like 22nd-27th just cause let's say someone on west coast of US would get someone from Australia it would basically mean a whole day earlier or later. Also there is countries where presents are opened in 24th and someone figured to post the picture in 24th morning of their time it would be still 23rd possibly on West coast of US... Just throwing it out there. Also I do know some people don't really want to be on to post stuff on Christmas though I think that might not be the case here by thinking how hardcore internet addicts most of us are.