Fun fact: the human brain can process speech considerably faster than the human vocalization systems can form it, so you can probably watch most videos on 1.25-1.75 speed wothout missing much, it just takes some adjustment.

At this point I cant watch people talking at a camera on anything slower than 1.5, because thats just the default videos play in (changed a setting on freetube and now cant stand slow), but I have watched 6+ hour videos that way. It cuts a substantial amount of time, and the speed up helps keep me engaged.