This isn't a big thing but.. In the session class $time_now is set at the start of the class (I guess to save some CPU) .. however the function time() is still used throughout the class ...

Since time() is used so much through out the all the code setting a time var in $this->ipsclass->time and only assigning it once in initiate_ipsclass() seems like it would be a good idea to save some cpu. Then you could do a find and replace for most of the time() functions and replace it with $this->ipsclass->time

I'll likely set up some constants for IPB 3.0.

This is not a bug in IPB but is more of a feature suggestion.