It's really hard to get a perfect match. I've never done it with a sponge so can't give much advice there. But when I've sprayed texture for patches I thin it to a pancake batter consistency. So I would try thinning your mix a little and see if that helps.
As for the drying times that can vary a lot depending on room conditions. If it's hot it will dry really fast. If it's cold it could take a longer time. Areas over heat vents will dry really quick with the warm air blowing over them.
As for the drying times that can vary a lot depending on room conditions. If it's hot it will dry really fast. If it's cold it could take a longer time. Areas over heat vents will dry really quick with the warm air blowing over them.