I recommend making a general list at the start of what assets you're going to need for the jam, then create placeholders that the programmers can use to get started with. For my own projects, I like to start with things like floor tiles, basic obstacles, and a character image so programmers can get a sense of scale for the map. Sometimes I don't end up with a lot of time left for animating, so I either have to skip animating certain things or throw something together without worrying too much about perfecting it. It's definitely one of the hardest things for me with game art in jams, I feel like I can throw code together a lot faster than good-looking art assets. You did a great job on the art, things will get easier with time and practice!