They seem to take somewhere around 3-4 years to go back into the water and a further year or two (or three in females) to reach maturity (at least in P. aff. fuzhongensis and P. deloustali).
The key is, in my opinion, to use a terrarium that is much (like 2-4 times) larger than one would use for a given number of morphs of other species and to use lots of leaf litter, cork hides in stacks, pieces of brick or weathered concrete to aid shedding (most deaths occur around sheeding, when infection set in if the morphs can't shed cleanly) and clumps of moss covering everything. A humidity gradient is imporant, with bone dry areas and damper ones around a small water dish. The dry area should never really be sprayed, but there must also be a good gradient (i.e. plenty of semi-dry/wet places as well as very damp and very dry). The morphs can either be fed in-situ and left to hunt or can be pulled out occassionally and fed separately, although this takes time to get working and then only in animals that have fully adapted to life on land. Avoid waxworms as I have had bad experiences with impactions. Once they pass about 6 months they become much more robust and after about 18 months to a year will start using a water dish and will gradually become more aquatic.
I wish you were in Europe, as I would love to give this species a go!
C