Sometimes, posts on a Message Board can happen in a thread months (or even years) apart, yet within a page of each other. Sometimes this is because the thread is merely slow, or the message board itself is slow overall, other times it can happen because someone revived a long-dead thread. Either way, you'll occasionally see someone respond to a post long after whoever posted it remembers what was going on in there. When this happens, timestamps are your friends.
Besides telling how old a post is this past year, it's sometimes useful to know how old a post is between years, and timestamps can help you there as well. Posting in a thread where two posts are literally over a year apart is rarenote , and often the result of extremely poorly thought-out Thread Necromancer tricks, but it can be very confusing if you're not looking at the timestamps.
In any online forum, it is highly advised that you pay attention to when the last conversation was taking place, and acknowledge any long delays in your message. It can greatly reduce annoyance for everyone involved, yourself included.