@poison_mara recently made a Workshop Thread for WIPs/concepts that arenāt quite ready for their own WIP thread- so short intros, proof-of-concept type things to test certain mechanics, etc. Basically just shorter stuff. I thought it was a really fantastic idea, so I thought Iād link it- thereās only a few WIPs posted right now, but it might give you an idea of what kind of WIP people think falls into the āworkshopā category.
I would say most WIPs that are āsuccessfulā (in that a lot of people read them and leave comments in their threads) are posted when they are already fairly long, so it takes longer than 5 minutes to play them through to the cutoff point. That isnāt always the case, of course- one of my favorite WIPs is only a couple of chapters right now, but I love the concept and the author is very active and regularly posts updates on their tumblr.