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.

Function:
1. Add clock appearance button to notify massage right-bottom that can add video to Watch Later Playlist.

How to use:
1. Click the clock appearance button.
2. Button will change icon after ask Youtube:
a. When response is success complete then button change to recycle bin, that can click again to remove video from WL.
b. When response is fail then button change to cross appearance, feedback to me , as long as I don't let YT stop me I'll fix it one day.