You can use multistream on Twitch just as any other platform. But if you have become an affiliate member of Twitch, the affiliate agreement doesn't allow simulcasting. However, you can start new content on different platforms after ending the one running on Twitch. For streaming the same content, you would have to wait for 24 hours after ending on Twitch according to the exclusivity clause. Otherwise, it becomes a violation of the affiliate agreement, and you might end up losing the benefits of a Twitch affiliate.