Darkness of dreams gives you around 20-30 minutes of playtime
Blue Moon doesn't really count much toward play time, its an extra area that lets you get secret items and uncover hidden lore.
Sorry if it's a little underwhelming, it was difficult fitting everything needed into the 2MB cartridge space.
Not counting the expansion packs, the entire game gives you around 2-4 hours of playtime depending on your style of play.
Thanks for your interest!