How do Twitch drops work?

Some questions:

Do they happen when whatching the game on twitch or just a certain streamers while they are streaming Legends?

What is the drop? Cards? gold? gems? packs?

Are they timed randomly? I just saw a post pointing out that it seems to have a 24 hours cool down. I would like to know if you get it after a fix amount of time watching or if they are timed randomly.

Can all people watching the stream get the drop or is it more like a lottery?

Thanks a lot