Custom Loading Screen

I have a roguelike I’m making at the moment which takes 2-5 seconds to load up the map when you start a new game (huge map, randomly generated). Is it possible to make it so that it loads some stuff first (instead of showing that white text x% on a black background) and displays that? i.e. Can I make a custom loading screen?

I’m trying to optimize the map generation, but it’s not even got everything in yet and it already is taking 2-5s. I expect in the end, a new game will be 3-10s to load.