Marathon Achievement

I’m an achievement collector, but I can’t seem to attain the Marathon achievement which requires the player to stay on the same server and map for 8 hours. I have tried it for 2 days already. I chose a map and set it to 2 players and idled for 8 hours but no achievement shows up. Please tell me if I’m doing something wrong or if there is a bug. FYI, I have already gotten the Half-Marathoner achievement.

Make sure you aren’t in the esc menu.
If that still fails, create a local dedicated server: