This was a fun little romp! My "first play" was 12:29, but that included resetting after about 7 minutes after not being able to get the second health upgrade in part due to the missing the first (Naturally, I made my way back there and turned out not to need it after getting the first one). So my "actual first playthrough" was indeed pretty close to 20 minutes all told.
If there's one annoyance I had, it was that on an XBox pad, Attack and Jump were indeed B and A respectively...except B is to the right of A, meaning the controls were reversed from what I'd call "standard Mario muscle memory". Luckily, I once speedran a game with that "reversed" control scheme, so it wasn't a huge adjustment. But it was one nonetheless.
That aside, this was very cool. I liked the GBC-esque visuals and the music. Recommend if you like platformers!