Indeed I tried and even though I can get a switch without any frame of UI showing, it is very hard to press and release fast enough. It's not a delay like I implemented, but most likely the UI being terminated before the next frame, so nothing shows.

In any case, adding a preference to change/remove the delay will satisfy people who want the UI to show faster (https://github.com/lwouis/alt-tab-macos/issues/8)