Hi Mary
It is really difficult to give an accurate time frame at the moment. It depends on whether you are having a paper-based review (rare) or telephone assessment.(common) Once an assessment takes place - the decision usually comes within 6 - 8 weeks.
You can always give the DWP a ring and ask about the status of your review. You might also ask why you were sent a review. However, whether a claimant has an ongoing award or not - the DWP can send out review forms whenever they like. I know a handful of people with ongoing awards who have had early reviews.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
