@Wishafish Not very far for people, not sure in snail terms!
It had to make its way out of a single narrow gap at the heater end of the betta tank and then cross about 4 ft of space over to the large tank. It then had to go up and presumably got in through one of the two hose cut outs. Must be happy in the large tank, it hasn't made any attempt to break out of that one!
Lost a nerite snail in my apisto tank. Made the fish's lives miserable by moving every log and rock in the tank looking for it, because a couple months beforehand, another nerite had died, hidden behind the sponge filter, and it caused an ammonia spike which killed a couple fish. This time, there was no sign of the snail. All water tests came back copacetic. About two weeks later, we found the snail. 2m away from the tank. Wedged between some floor boards that were under the sofa.