This is now fixed. Basically, there is an issue with the core forum install that makes it think that it is in the US, despite the fact that the forum is set to GMT....thus it being 5hrs behind.
What we have done is a tiny bodge, were all users are now set to US eastern time and that has resolved it.
You can change this setting back to GMT in your user settings, but that will then cause the same issue, so if you see you are set to Eastern -5hrs, leave it be.