Is it possible to add an entire playlist to my
Watch Later list? Usually not an issue but this playlist has 62 videos.
I'm not aware of a way of doing this via the youtube UI (website). However you might be able to use the Youtube API. Access to the watch later list was introduced only in v2 of the API, v3 should also work. Note that since it's a private playlist you can only access it via an authenticated request.