With any new release, as soon as the flag is lifted, all the servers will quickly crash because all players will be racing to the login server. It's happened for every major MMO release. WoW was nearly unplayable for 2-4 weeks. Oh, I remember all the free game time they gave us. =)
The holidays will help and hurt Bioware. It will help, as you pointed out, by allowing people to login more sparsely than during "primetime" like hours. It will hurt because it's almost assured that the servers will be down, there will be hundreds of thousands of people foaming at the mouth to play with gleeful excitement, having ALL HOLIDAY to play, but can't because of server stability... oh, the forums will be aflame no doubt!
I'd like to be positive and say "Bioware is spending gobs of money on this game, they have WoW and piles of past MMO launches to draw experience from, they surely WILL get it right!" Yeah, I said that about every MMO that's come out and I don't recall that ever happening.
For starters, they'll probably have lots of server/shard capacity (they're pre-selecting servers for pre-orders based on allowing you to pre-create a guild) but they'll severely under-power their login server so that only a few lucky people will login and have fun while everyone else is crammed in the door, pushing and shoving to get in, until the whole door collapse and no one can get in.
It will take a couple of days before the rush to play spreads out, but not before login servers are added and rebooted, and people get so fed up with trying to login the go and do something else.
At that point, they will have major lag issues because no matter how much stress testing they do, they will miss something in the code that will thousands of players playing, will cause the game to crash. So, they will be spending the first couple of weeks pushing out patches to identifying issues to bring server stability in-line.
It always has happened. Never fails. =)