Comment by maxerickson

Here's a sort of solution, a bookmarklet:

https://gist.github.com/maxerickson/8456792

It turns the timestamps into collapse buttons. It's sort of adapted from here:

http://alexander.kirk.at/js/hackernews-collapsible-threads.j...

I have another gist there with a bookmarklet that turns the timestamp into a button that hides comments of that age or older.