IANA judge, but here's a prior response from Otto:
"I would say people should be able to get the gist of the game within 15-30 minutes." - https://itch.io/post/4748276
I would take this as an indication they'll be playing the games until they get an idea for how the rest of it will play out and 15 minutes as being the rough upper-limit for how long it'll take to reach that point (and longer if they enjoy the gameplay to keep going).