Craft Cookies Plugin: Font Loading Detection
So I'm not sure what you're accomplishing with this line:

    {% do setCookie('fonts-loaded', fontLoad, now | date_modify("+1 hour").timestamp) %}


I guess trying to give the cookie a longer duration if it was already set? Probably it's best to set the fonts-loaded cookie via JavaScript once FontFaceObserver tells us that the font as been loaded; there's probably no reason to do it here.

FWIW, we can start using the font-display property as a progressive enhancement now to want to eliminate FOUT on modern browsers. Older browsers will still work, but they'll get FOUT: https://caniuse.com/#search=font-display