You've always been able to hack a YouTube URL to seek to a specific time, but now all it takes is a right click.
This is a very simple trick. Load up any YouTube video, seek to a specific time, pause the video, and right click. Then you'll be able to choose "Copy video URL at current time" and end up with a URL that'll start the video at the time you chose.
Thanks for the tip, HahSohrob!