How to tell which friends have been inactive?

by Valeriel posted Jan 27, 2018
Since the friend list caps at 50, I always find myself needing to delete people off my friend list to add new friends. What's the best way to tell if people have been inactive? Should I check the arena friend ranking list and delete the lowest ranked? When I go to my friends list, I also see a time stamp next to their name that says "over a week ago" or "2 hours ago" or something like that. Is that indicating the last time they played? It seems inaccurate so I'm not sure.

I try to keep the people that are constantly using me in their ruin runs to get the bonuses.