Later this week, Time Rifts will open for testing on the PTR.
This week, testers will be able to play through stage one of the Time Rift event. Stage two, which is coming in a later build, will take you through a portal into the alternate timeway from which the incursion is coming. When you complete stage one on the PTR, you should get a message saying that this is all that is available for testing.
Initially, testers will see invasions from the murloc world of Azmerloth and from the Titan-inspired world of Ulderoth. Future PTR builds will include incursions from other worlds.
Thank you for your testing and feedback!