Eh, I think it's fine if said timestamp starts off as relative, but becomes an absolute timestamp after a while. For instance, quite a few forums I use have the

Eh, I think it's fine if said timestamp starts off as relative, but becomes an absolute timestamp after a while. For instance, quite a few forums I use have the timestamp for today's posts as 'posted today at [time], but it changes to 'posted yesterday at [time]' when its a day old, then eventualy to 'posted on [date] at [time] once it's about a week ago or so.