No worries about them maturing unwanted. There's a thread in one of the breeding forums where someone worked for months, going through hundreds of larvae before obtaining a single adult. They have to survive for about 3 months in the water column, getting enough to eat while not being eaten themselves, before they touch down and begin walking... needless to say they'll probably either lose an encounter with a fish or pump before then or starve. Their lifespan in an aquarium is probably measured in hours (and many not even that long).