When I am using Facebook on my PC, on the chat bar I see last online time for some of my friends. But I don't see last seen for some of them. Why does this happen? Is it because the person has turned off chat for me or does the time appears of those who have Facebook in their phones? How do I keep others from seeing my last online time?
I believe it is because there is a time frame set automatically. From what I have noticed is that if someone has been off chat after the 24 hour mark, the time automatically stops accumulating. The only thing you will see at this point is the person's name only. I have paid attention to this pretty good so I am confident that this is the reason. In other words there is not time displayed beside a persons name after 24 have passed since their last chat log on.
The last online time is typically shown based on when they are last online on the chat from their phones as indicated by the little cellphone symbol beside their last online time.