The jam lasts for 2 months. From March 15th to May 15.
The idea is that making such a small game over such a long period should keep everyone from needing to crunch.
Premade assets was more in reference to the tools you've got on your belt already, like I often use the same text reader script and pine tree sprite I made 5 years ago in every game cause they're well made.
However, I'm not going to remove your game from the jam just because you decided to start working a day early. It's not that serious.