I wouldn't be surprised if they have such as system on itch.io since they host so many jams. In a database (which this whole jam is in essence) a simple cluster analysis (common method to determine insurance fraud) would uncover every suspicious transaction (in our case rating) instantly. I simply don't know if such a tool is available to the hosts, since I never hosted a jam myself and have no clue about the back end.
But I would never implement a hard timer. Not only would this give you tons of false positives, it is just going to make some people pissed.