TBH you can do anything even pre-made assets! It's more the code of the game I'm more worried about being within the jam limits! However there is enough time to flesh out some graphics that are not pre-made! Just remember the game as itself has to be made in the jam, not necessarily the attachments it runs like audio or graphics! Meaning if you wanna go hardcore into coding up a game that works with minimal bugs and errors then placeholders are fine! I will likely make an RTS game Jam 2 for you to furthermore tweak a pre-existing game from this game jam if for some reason people are running into complications but if only 1 or 2 people have issues then a 2nd game jam unlikely but if lets say 7 or more then very likely! An RTS can be as simple as Minecraft or Flappy bird which those were made less than a week for games! Meaning just whip something up then tweak later haha :)