FWIW I just did the Xbox upgrade immediately (Destiny)

by stabbim , Des Moines, IA, USA, Tuesday, September 09, 2014, 23:25 (3526 days ago) @ petetheduck

That was pretty much my experience. Up at 5am (might be same time, I don't know where you're located), started 360 download, turned on the XBone and started that download.

I unfortunately forgot to check the XBone's auto-off timer (I have no excuse for that, after all the 360 did that as well) which meant it only got to about 40% before shutting down. Luckily, I work at home and was able to check it during the day. Both consoles were ready to go well in advance of me getting off work at 5:00pm. I was even able to start the game uip during lunch to let the updates download.

FWIW to anyone, you really can just put down one console and start playing on the other, and all your gear, mission progress, etc., is up to date. I imagine it probably won't let you play both at once (and that's a good thing, considering how out-of-whack your saved state would get). There is another bonus: apparently, which achievements you've unlocked is part of the game data saved on Bungie's end. Meaning if I get a few on XBone, later when I log on via my 360 I get a bunch of 360 achievements popping. So regardless of which console you do things on or which console your friends use to look at your achievements, they'll see an accurate representation.