This isn't about hours or day and night, it's about the course of events, and your place within.

It is impossible to know of an event after it has happened, unless one is psychic, or has been informed of it. If you arrive at a location after an event has happened, then you logically and realistically should have no idea about it, correct? Correct.

Thus, there should be no posts saying ::So and so walks in and overhears/sees whatever happened about three hours ago world time.::

That sort of thing simply does not work when we're writing in the present tense. It's understandable that users wish to get in on the action if something particularly exciting is happening, but understand that if an event is over, it is over, and you cannot reverse time to compensate for you not being online when said event was happening.

However, you may use the past tense. This is allowed, but please don't go in excess. Usually, you should only use it when your character is already in a thread but hasn't posted for a long time, for example:

::Character had been listening intently to the other's conversation up until now, when she finally pipes up with an opinion of her own.::

Still, you may use it if you really feel you wish to have been witness to an event, for example:

::Character had arrived on the scene just as the hideous beast was about to attack it's victim, but had watched from the sidelines. Now she creeps from her hiding place, trembling, and hurriedly checks out the area for any signs of the monster's return.::

If something doesn't make sense in real life, chances are it won't here either!