48 hours is the time you have to make the game. For example you can spend 5 hours every day for 9 days and that's about 48 hours
or you can pull 2 all nighters and use up all your 48 hours. It's a 9 day jam but you have 48 hours to make the game.
"You have 48 hours (don't have to be consecutive) to make a game"
At least that's my understanding please correct me if I'm wrong
Hope this helps
I think it comes down to trust. It's not fun to cheat. You can tell and if you got caught then you have a chance of getting banned from jams. It's not worth the risk. Most people will follow the rules because they like the challange and it's unfair to cheat when others are following the rules. Even if you cheat you won't nessarsariy make a better game. Game jams are about doing a lot with little. The creativity wins over the polish most of the time. They also want to make the jam accesable. Just because a few people cheat doesn't mean they should punish everyone