On the actual PM it doesn't say the time of said message, only in the Inbox. This is particularly a problem in PM trees, where time stamps matter more, as there are multiple messages associated with that PM. Also, a PM tree does not move up the "queue" in the Inbox with each new message. Like, I have a PM tree that got new messages today, but if I want to access it through the inbox, it's sitting on page 3 alongside PMs from February. It gets hard to browse each time you want to look it up.