From my tests. After 3 hours continously, I started receiving only 75% of the reward for killing npcs. A 20 minute break didn't reset it. After hours it was resetted (not sure how long I had to be off for it to reset).
Palla, gates and BL maps don't seem to be affected by this. (I only tested palla and can confirm that there is no punishment after 6 hours on palla, but about the gates and BL maps I read on a discord server).
Maybe someone tries the 10 minute break every hour strat and let's us know how it goes.
3 hours is so very little, I used to play this game for 6 hours straight without getting up, I guess BP cares about our health too. Anyway, this is just a small bump, it won't stop us from botting this lovely game. As long as we can bash gates, we'll be on. This is once again going to only annoy new players (do they still exist? I feel like only those who started playing 10 years ago are left in the game)