This wikiHow tells you how to see when your friends were last active on Facebook. This works well when they are also logged into Facebook Messenger.
Steps

Step #1. Open Facebook
This is the blue icon with the white 'f' in your apps folder or on your home screen.
- Log in if you have not already done so. Enter your information and tap login.

Step 2. Tap the icon for your contacts
That's an icon at the top right with a human figure and three horizontal lines.

Step 3. Scroll down until you find the person you are looking for
You can view everyone's last time online in the 'Top Contacts' list on the current screen. There you will also see a list of friends who are currently online. To the right of their name you will see the time.
- A green circle next to a person's name means that he or she was online now – or in the past few minutes.
- A number followed by an “M” (minutes), “H” (hours), or “D” (days), shows the number of days, hours, or minutes since he or she was last active on Facebook.