Today is Day 21 and one chick has made it early. It can stay in the incubator for at least 24 hours before needing water. At the end of the day it was moved to the brooder box and I dunked its head in the water. It will find the food itself. Despite a very hot day I turned on the lamp attached to a timer so it has some warmth all through the night. There is some more cheeping from the remaining eggs so it may have some peers by the morning.
Maybe I have solved the problem - time will tell.