Re: R. imitator froglets
In my experience with ranitomeya I wait until the front legs emerge from the body at which point I leave the small cup with the froglet containing about 1 cm of water at a 45 degree angle inside a larger container filled with soaked sphagnum moss and tiny bit of leaf litter. I've noticed froglets will come in and out of water during the period of the tail disappearing. In case they leave the cup early the soaked sphagnum will keep the humidity >90%. They will usually not eat for 3-5 days after emerging from water and with the tail gone.
Steve - NorCal - R. variabilis highland, imitator Yurimaguas & Varadero, fantastica "true nominal"