Hover a thumbnail on youtube.com and click an icon at the right: "Not interested" and "Don't recommend channel"
< Valutazione su YT: not interested in one click
I'm not sure it's a good idea to change the site's behavior/timings. Personally I've simply disabled this preview. There is another userscript that can do the same when clicking with Ctrl or Alt key, so maybe you'll like it more.
extend .ytp-inline-preview-scrim (video hover preview) timeout to click successfully?
transition: opacity .2s cubic-bezier(0.4,0,0.2,1) .1s;
transition: opacity 2s cubic-bezier(0.4,0,0.2,1) 1s;