@poison_mara recently made a Workshop Thread for WIPs/concepts that aren’t 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 I’d link it- there’s only a few WIPs posted right now, but it might give you an idea of what kind of WIP people think falls into the ‘workshop’ category.
I would say most WIPs that are ‘successful’ (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 isn’t 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.