I have successfully bred my mystery snails. The egg sack must be out of the water, or the eggs will drown, and not hatch. It takes about 2-4 weeks for the eggs to hatch, and be prepared for tons of babies! I had over 100, but I only have 8 now, most of the babies died of starvation, I believe. And, google is good too (most of the time)
When in doubt, Partial Water Change!
75 gallon ~AquaClear 110, Harlequin rasboras, Cherry barbs, Tiger barbs, Otos, Kuhlis, Rainbowshark.
10 gallon ~AquaClear 30, Guppies