See My Thumbnails Appear the Fastest?

There are four choices, and the one that will make your thumbnails appear the fastest is to choose Minimal from the Build Previews pop-up menu, at the top of the File Handling panel (in the top right of the Import window). It just grabs the small preview that your camera has already created, so it doesn’t have to do a lot of rendering—it just shows that thumbnail lickity-split (I always choose Minimal myself, because I have a severe lack of patience).