Looks like they delayed the beta for everyone who hasn't already started playing
:
Rainbow Six: Siege open beta delayed

Ubisoft has delayed the Rainbow Six: Siege open beta, which had been due to go live today.
Notice was only issued of the delay within the last hour - a short time after the open beta had been due to go live.
"We're currently seeing issues with matchmaking times and disconnection on all platforms," community manager Jax explained via the Ubisoft forum.
"As such we're postponing the Open Beta until a later time and keeping the game under Closed Beta status. We apologise for the delay and can assure you this is our top priority. We will keep everyone updated regularly as we continue to deploy improvements."
Rainbow Six: Siege open beta delayed