Hah! I've just come across a bug in msgpad that is a minor annoyance. The problem is that I print the posts in sequence, and weave time interval markers between the posts. So you could have a few posts and then something that says, "2 minutes ago", and then some more posts and then another marker that says, "5 minutes ago". Something I hadn't considered is that everyone's clock is out of sync, and being out by a few minutes is not unlikely!
The HTTP packets returned to the browsers contain the server's date so I should be able to calibrate. Even better though, you won't need to have your time/timezone set correctly for the relative time markers to function. Still, something I never really thought about before now...