So whether or not I submit a game, whatever I make would probably use royalty free sound effects. Maybe this doesn't matter, but would searching and selecting sound effects (or any other free assets on the internet) be considered part of "coming up with ideas" or "development time." I'm asking because it makes the difference between losing dev time or not.

opinions differ a bit on this one. some say, it counts, some say, it doesn’t count, if it’s your local asset library, some say, it does never count, but WHAT counts is, when you start modifying your assets (like resizing images, recoloring, adding echo/fade effects to sound, normalizing them). this is then work on assets specific for that game.

searching your harddrive through thousands of images while waiting for a theme/an art style that inspires you, may be seen different.

bottom line, trijam is a honor system. if you feel, that you’re overboarding your “research time” and feels like cheating for your inner voice, be honest to yourself and the other jammers, and count it.

Grisgram gave a really good answer! But usually preparation is more like pre-production. You might as well build the game before to understand your workflow and then do the production as part of Trijam. The point of Trijam is to improve planning, focusing and execution under time constraints. It's surprising how much can be done in 3 hours when you know what and how you have to do!