You might want to have a read of my cluster technote....find it here....https://support.arubanetworks.com/Documentation/tabid/77/DMXModule/512/Default.aspx?EntryId=7961
But to your Q's - The 2-hours depends heavily on the size of your DB's. In the 6.6.1 release notes is a section with a few use-cases to provide some guidance on timings.
Users don't 'go-over', once they are authenticated. It will depend on how your NAS's are setup. IF say a switch/Ctrl is has a primary NAS as A and secondary of B then assuming the capabilities in AS A support fall-through you should be good... you might thave the ability to have a VIP between the two boxes then it makes it easier as the VIP will 'move' to the SUB [assuming L2 domain] when the PUB is down so NAS just goes to same IP all the time.... it depends heavily on CPPM clustering, how your NAS is configured and the capabilities of the NAS.