The Moment
For those still confused about how to resolve The Day of the Doctor with The End of Time, it’s actually all pretty clean and tidy.
The Time War is sealed away so (in principle) it can’t be undone; we’ve now seen two different stories set in part on the exact same day; the final day of that war. The two stories give different perspectives on some of the same events.
Notably, both stories involve characters — Rassilon and the Moment — puncturing the Time Lock to try to avert Gallifrey’s destruction.
Rassilon did it the dumb way. He tried to pull Gallifrey out of the Lock, to continue the war. Shortly after, the Moment pulled the Doctors in, to end it.
In The End of Time they state that the Doctor has just taken hold of the Moment, and intends to use it. Ergo, the events of The End of Time occur in direct response to John Hurt’s actions at the start of The Day of the Doctor and take place while he is walking across Tattooine with Rose Tyler slung over his shoulder.
Of course Rassilon’s plan is crazy, dumb, and a failure — so in The Day of the Doctor a minor character later dismisses those events in a throw-away line. Rassilon’s failed plan is a minor thing that happened on that day, off-screen, involving power-mad characters who don’t factor into reality.
Then the Doctors all swoop in to save the day, sort of. Meanwhile, one presumes, Rassilon and the Master are still busy hopping all over the High Council chambers, shooting lightning bolts at each other.