Final update:
YouTube delete my account,so I don't use YouTube with log in after this.
Keep this script for download before user feedback it not working,
then I delete after not working.

Description:
1. Sorting playlists by play time length use internal API.

How to use:
1. Install this script.
2. Open Youtube use web browser.
3. Switch url to a playlist, like: "https://www.youtube.com/playlist?list=WL" .
4. Click new button display as "Play time length" one time or two times that sorting by raising or lowering.
5. Wait for progress bar on "Play time length" button.
6. Web page will auto refresh. (If not, please refresh manually by yourself.)
7. Done.