You can go 1 full week in the rain chamber with no food. If no eggs take them out of the tank and feed them for 1 full week...then try again a week later =)
Took me about 3 times before they actually laid eggs...IT WILL happen...just be patient. You have a really good rain chamber I have full faith that it will work...keep us updated.
ALSO as soon as you have eggs remove the adults... and stop the rain system. (if you do not the rain drips will kill the eggs) -OR- you can cut the leaves they were rained on and put them in a seperate tank by taping the leaves to the side of the tank. 10-20 gallon tank would be best. IT IS CRUTIAL you maintain humidity in the tank so make sure you cover the top with something (preferably glass) to maintain moisture so the eggs do not dry out. I found an automatic fogger works REALLY well to maintain humidity. Misters not so much. If your eggs are not fertile they will mold over within the 4th day) You will see development on the eggs on the 3rd day anyway.