Why don't you detect the time zone from the user's profile (perhaps a state abbreviation and country code) and match it to the time they make a post and display others' posts?
Also, php programming is WAYYYYYY behind what microsoft.net technology can do for an extensive application such as this forum. You should sometime consider hosting this on a Windows server that can take advantage of the rich and robust contemporary environment of .NET framework
Also, php programming is WAYYYYYY behind what microsoft.net technology can do for an extensive application such as this forum. You should sometime consider hosting this on a Windows server that can take advantage of the rich and robust contemporary environment of .NET framework