You generally have a two hour window to return to ride RotR so you can use your FastPasses as scheduled and not have to worry. The exception seems to be the first set of groups called. They only have a one hour return window. Even with that, if you miss your window because you had just gotten...
When you sign up for email updates they tell you to be sure to opt in to "Walt Disney World Resort (from Disney Destinations)". Not 100% sure that answers your question.