If you’re using a Twitter client such as HootSuite, you can easily see the exact time that a tweet in your feed was posted, as HootSuite conveniently displays the timestamp above the message. Other clients work in a similar way. On Twitter.com things are a little different. There, Twitter prefers to show you how long it was since a tweet was posted. For example, it might say 55 seconds ago, 19 minutes ago, or 1 or more hours ago.
At one or more hours, Twitter.com tends to clump tweet timestamps together, so you get many tweets showing the same timestamp (i.e., 2 hours ago), even if they were posted at very different points over that hour. And when you move to a day or more, Twitter.com displays 1 day ago, or 5 days ago, but doesn’t tell you anything about the time at all.
So how do you find out?