Alt+Tab show-up speed is too slow - can I make it instant on Ubuntu 17.10?

To fix this you could install a GNOME Shell extension. You can find a short tutorial on how to do this here: How do I install and manage GNOME Shell extensions? or this external link.

Basically once you have installed the GNOME Shell integration add-on for your favorite browser and the GNOME Shell integration for Chrome on your system - go to extensions.gnome.org and search for

Alt-Tab Switcher Popup Delay Removal by xhfhope

or go directly to

https://extensions.gnome.org/extension/1317/alt-tab-switcher-popup-delay-removal/

and install the extension (you should only need to click on the switch and turn it "on"). Now the Alt-Tab delay should be gone.

I don't even understand why this delay exists. Basically, what the extension does is the following (I'm not the author of this extension):

function init(){
    defaultValue = imports.ui.switcherPopup.POPUP_DELAY_TIMEOUT;
}

function enable(){
    imports.ui.switcherPopup.POPUP_DELAY_TIMEOUT = 0;
}

function disable(){
    imports.ui.switcherPopup.POPUP_DELAY_TIMEOUT = defaultValue;
}