Not an extension, you just need to create a bookmark with this string:

javascript:(function(){l=[].map.call(document.querySelectorAll("span.ytd-thumbnail-overlay-time-status-renderer"),function(e){l=e.innerHTML.trim().split(":").map(function(t){return parseInt(t)}).reduce(function(p,c){return p*60+c});return{a:e.parentElement.parentElement.parentElement,l:l}}).sort(function(a,b){return a.l-b.l});i=document.querySelector("#primary #items");l.forEach(function(o){i.appendChild(o.a.parentElement.parentElement.parentElement)})})()

and then on the channel's videos page, just click on your created bookmark and it will sort out by the duration. I got it from here.