When you are moving the shot times around you can split the hour changes up over a couple of cycles. So start moving it a cycle or so before the full change is needed, then change back over more than just one cycle. Changes 1/2 hr per cycle are ideal but changes of an hour per cycle should be OK too. And if you had to do the full 2 hours in one cycle, it should be acceptable - I think Joanna had some good input on that earlier for you if you did need to change up to 2 hours in one cycle.