Linear Predictive Algorithm?

Ok, here''s what I want to do: I want to have my world-time guided by the system time (or my own time system). And what I''d like to have happen, is when the player loads his/her game it takes into account the amount of time that''s passed since they last played, character behaviors, etc. and make things change appropriately in the world. My game is being done in C++, with STLPort. If anyone could point me in the right direction (lots of examples for me to tweak and play around with would be great), please do! Also, if my needs are confusing, just let me know what information you need and I''ll be glad to give you as much as I can (I''m still in the planning phase).