I've killed King Chuck during the recent March 2020 Orcsoberfest event numerous times. During this time the cool down was not as what was intended. We were advised the cool down for King Chuck was changed from once every 20 hours to once every hour, but only three times in 24 hours for just 100 points each success.
However, I had an issue where I would kill King Chuck 3x within a day, at 9 AM, 10 AM, then 11 AM for example. Then the next day I would try to kill King Chuck at 9 AM because 24 hours passed, it didn't work. I had to wait until 10 AM that day to kill him I believe somewhere around there. Also, another issue was if you went to kill King Chuck but only killed him twice during a 24 hour period then the next day you were only able to kill him once and then the cool down started after that last kill.
I asked the CMs on the Tibia forums what the cool down was because I was having issues as it wasn't the 24 hours as stated in the news. Mirade, a CM, advised me that as per what she was told from a Dev, the cool down starts the moment you push the lever for the first time. Other players were experiencing this issue and advised us typically the cool down was you kill the boss 3x within 24 hours, 1 hour between each kill at least. The next day you had the opportunity to kill King Chuck an hour after the first time you killed the boss. This seems to be an unintended bug with the cool down for King Chuck. Skerio, one of the CMs is forwarding the issue with King Chuck to the testers so they will look into it. I'll edit this when they resolve the issue with the cool down for King Chuck.