Should be streaming ot recording?
It wouldn't neccesarily be something like "I'm gonna spend all 9 days working no-stop to win this thing!", althoguh I would imagine some people doing something like that...
But imagine your timer says 46 hours and 50 minutes and you forgot to make a pause screen or something. Then it'd be like "oh well, 48 hours and 57 minutes, it doesn't matter". It's much easier to fall on a trap like that, so yeah...
I think he just trusts you, that you don't cheat and don't abuse the rules.
But if you want to make sure, that you spend 48hours, you can track the time you spent by yourself by enabling a stoper when you work and stop it when you stop. Then save these times somewhere and just sum them up. If it's below 48, you have time. If it's in the 48 hours frame or you have a little bit more than that, that's it.
Also, you can just record it(well.. 48 hours of video footage might take some disk space) or stream, as you mentioned.
Honor system. But also if you actually need more than 48 hours you're almost certainly not gonna win. Most of the best entries in the video series were made significantly under the time limit. E.g. Stuffed Wombat's game was made in only 4 hours one afternoon and was probably the best one in that video.
I think if everyone here was a full-time indie developer, there would be a much smaller crowd. Indie developer can mean many things, but a lot of the time to be successful it means putting a hold on side-projects and working on the project that pays (assuming you don't make money from something like YouTube showing off side-projects). Jams like this are mostly designed to incorporate everyone who loves game development, but maybe doesn't have as much time. I would't worry! Besides, a good point was made that the best games from these art-pack videos are the ones that are made in the shortest amount of time. Just a simple and fun concept stretched out as much as possible. If someone makes a game that was done in more than the time limit, it's usually painfully obvious.
Many game jams you can't separete time for personal needs from game dev, so if you consider Ludum Dare that have 48h, if you subtract 8h of sleep for each day and 3h for others needs you get around 26h (or only 10h if you have a 8h work in the days of the jams) in total for making the game. In 9 days would be almost 3h/day.
But anyway, hope you have enough time to make your game, even if you end up not using the full 48h ^^