i thought i might release the baby snails in the allotment near my house
No offense of course, but I seriously hope you are joking. Why would you release something that is NOT native, into the environment? I know nothing about these snails of course, but why would you do that? Supposing these snails develop a taste for a certain plant, that up until now, while being eaten by native snails is doing well, and supports a whole microcosm of life, which in turn supports a whole different species or two. These snails you just released eat all the plants that 100's of other varieties of life depend upon. These other varieties then die and are now extinct. Gone. Never to be seen again.
Now, these snails you released have multiplied into 12,000 snails, who continue on eating plants at an amazing pace, and wiping out entire ecosystems as a result.
Please, please, please, please, please, dispose of your snail eggs or baby snails in a responsible manner. DO NOT release them into the environment.
Even if they will die in freezing temperatures, please don't release them. You never know what can happen in nature. All it takes is one freak snail to survive a winter, and then disaster strikes.
ETA: I do think your snails are quite lovely though. Nice pics.