The Back To The Roots mushroom kit produces very nice brown oyster mushrooms within a few days of rehydrating the substrate. Since hydration is the primary limiting factor for producing good flushes from kits, it is recommended by this grower that you remove the substrate completely from the mycobag, then submerge the substrate block overnight in clean, cold water.
https://www.amazon.com/Back-Roots-Mushroom-Mushrooms-Gardening/dp/B00TUYGRU4

