I don't know if there is a wait time for newbies. When I post a YouTube link, it shows up right away. If you want to embed the video, you have to use the URL of the YouTube page that the video is on. Using the URL that YouTube provides when you click "share", doesn't embed the video.
For example, this is what happens when I just paste the "share URL" into my reply:
This is what happens when I link it:
And this is what happens when I just paste the URL of the YouTube page with the video:
I hope that helps.