Sometimes I come back to iMessages on my iPod after having received multiple messages from the same sender, and want to know the time that a particular message was sent.
Timestamps of messages can be found with a swipe in iOS 7. In iOS 5 (and, I suspect, iOS 6), there is also a way to find the timestamp of any message in an iMessages conversation. In some cases you must delete surrounding messages, but you could copy their content elsewhere first (long-press or double-tap a message, and Copy), if you needed it (I myself rarely need such).
(1) If the message for which you want the timestamp is from "today" (after the most recent midnight), then:
(1a) If it is the last message in the conversation, you can go ("back") to the Messages list to see its timestamp.
(1b) If it is not the last message in your conversation, then:
(1bi) If it contains a string which isn't found among the conversation's other currently loaded messages (or if found chronologically first in your target message), go to the Messages list, search for that string, and you will see the intraday (hours:minutes and AM/PM) timestamp there. As needed, you can "Load Earlier Messages" at the top of a conversation; those are cleared by quitting and loading the iMessages app again.
(1bii) Delete other, later messages from the bottom up, until it newly becomes the last message in the conversation, then see (1a) above.
All of the above ideas except for (1bii) were mentioned on http://apple.stackexchange.com/questions/32408/can-messages-display-the-timestamp-of-every-incoming-message, which was the best solution I had found before doing the investigation which led to this blog entry.
The next method is not limited to messages from "today". Every message has timestamp data, but iMessages only shows that to you under certain conditions.
When you start exchanging messages, that delineates the beginning of what I call a "snippet", which is a piece of your conversation (someone else referred to this as a "chunk"). iMessages identifies that with a center-justified snippet header which shows both the date and time. After some period of inactivity (15 minutes? That's someone else's guess; I didn't research it.), iMessages will end that snippet. Subsequent messages between you and the other party will generate a new snippet with its own snippet header.
By deleting earlier messages in a snippet, you can update the snippet header to show the timestamp of the first remaining message in the snippet. Not exactly obvious, but that's how you can find the timestamp of any message, no matter how old.
