You can choose who sees this info in Privacy and Security settings.
Remember that you won’t see Last Seen timestamps for people with whom you don’t share your own. You will, however, see an approximate last seen value. This keeps stalkers away but makes it possible to understand whether a person is reachable over Telegram. There are four possible approximate values:
- Last seen recently — covers anything between 1 second and 2-3 days
- Last seen within a week — between 2-3 and seven days
- Last seen within a month — between 6-7 days and a month
- Last seen a long time ago — more than a month (this is also always shown to blocked users)