Cool lid/spillway. I grow/hatch mystery snails, the method you are using is the second best I've found. The first best is leaving them where they put them. The issue with your method is that the bowl is likely to be either too dry, or too flooded. With a bowl too dry the snails will starve and dehydrate before they make the trek all the way to the water. Think ant man, time-space grows as you shrink, these little guys come out the size of a fingerprint groove, crawling all the way across that dry foodless bowl is like walking across the state of Washington.
I've had good luck relocating the eggs to lily pads and other floating plants if I was worried about predation but usually the dirty/algae dripping humid areas on the glass lids are what works the best. If you want to improve the floating method, try finding a smaller floating item you can drape a paper towel off the side of into the water. The water will wick up the paper towel, set the egg clutch right on top of that. You can get some bonus in if you can scrounge up enough algae to turn the paper towel green (use it to wipe the lid above an air stone maybe) and use it that way.
Finally, not every clutch will have a good hatch rate, sometimes the eggs are just outright dormant. It can happen, I had 3 of my last 5 but hatch well, but the most recent one hatched at a near pest snail rate. I haven't figured out what causes this (it's only my 5-6th full generation) but nature has been pretty good at finding a way.
Here's a shot of a fresh hatched baby. If you need to help them into the water remember to use wet fingers and be careful not to roll/crush them as the operculum is very fragile at this size.
