http://www.pcgamer.com/sea-of-thieves-closed-beta-extended-by-two-days/

The Sea of Thieves closed beta arrived yesterday, but many players who were granted access after pre-purchasing Rare's first-person open-world pirate game found themselves unable to play. Instead of being able to install and launch the game, many hopeful swashbucklers received an error message stating it was "too early" to play and were locked out. Rare rolled out a temporary fix today and is working on a longer term solution, and to compensate for the trouble the closed beta has been extended by a couple more days to ensure players get enough time in the game.

The beta, originally scheduled to end Monday, will now finish on Wednesday, January 31, at 8am GMT. If you've got access to the closed beta but are still having trouble getting in, Rare has posted instructions on how to install the game via the Xbox Insider Hub.