If you pause all of your games before backing them up, they should be *mostly* unaffected by time changes. There is no way to completely isolate savegame backups from the effects of clock changes, because the game determines what to do based on when the game was last saved, what the game speed setting was, and what the current system clock setting is. As long as the games are paused, they won't be ruined by time going forward from when they were last saved. However, certain facets of the real-time engine can be adversely affected by time going backwards, even when the game is paused.