How might our RAC and DataGuard DBs cope with time travel?

Our UAT guys have come up with an interesting requirement. They want to 'time travel' their UAT environments. By that we mean roll the OS clock forwards to dates in the distant future to test the application. Now, that in itself is fine. We have a couple of envs where we do this for them in ring-fenced, 'normal' environments that comprise only stand alone, single instance databases.

However, they now want to time travel one of our full-size envs which has multiple RAC 10g and 11g databases, some with DataGuard logical standby databases hanging off them. All across four nodes.