Adding a time stamp on post view

You are nearly there, I’d say. I am sure there are many ways to do this. If it were me, I’d build a ‘nested’ array for this. Something like…

array(
    'timestamp-1' = array(
        'message' => 'Updated post1',
        'message' => 'Updated post1'
    ),
    'timestamp-2' = array(
        'message' => 'Updated post3',
        'message' => 'Updated post4',
        'message' => 'Updated post5'
    )
)

… where ‘timestamp-N’ is midnight or midday or some arbitrary value for a particular day. You can run wp-cron daily to check the array and clean it up. I suggest doing it this way because using a minute-and-second timestamp means having to check and manipulate that array pretty much every page load.