Answer Question
There is a third party trick to disabling this optionhttp://time.com/3692029/facebook-tricks-tips/Maybe they did that
What does the "Last Active" time stand for on Facebook Messenger mobile app?
How do i hide "Last Active" time stamp facebook messenger mobile app?
Is there a way of turning off the "last active" in facebook messenger?
Can the last active time on facebook be wrong?
Who can see my last active status in facebook messenger?
Facebook messages/friend last active?