In iOS 6, the Messages app will show you when you started an exchange with someone, and it will remind you of the time you chatted periodically thereafter, but it won’t show you the timestamp for each individual message you send or receive. iOS 7 keeps track of timestamps for individual messages, and it will show you them—provided you know this simple trick.
Open the Messages app and navigate to a conversation thread. Once there, make a swiping gesture onscreen by swiping your finger from right to left. As you swipe, the timestamps for each message will appear. Lift your finger or slide it back to the right, and the timestamps will hide again.
Unfortunately, iOS 7 doesn’t let you always show timestamps for all messages, but at least the info is there if you need it.