While plating your parts, you can also plate a piece of copper wire from house wiring at the same time. Using a micrometer on the unplated part of the wire vs the plated part, you can see how much zinc you've deposited. Divide by 2 since you are measuring 2 sides. Commercial plating thickness is in the range of 0.0002 inch on one side. So when you get about twice that thickness you know you've done about all you can do.

The Cronak dip is a slow drying gel. That's the reason for the heat gun. After drying with the heat gun, hang the part up for a while or a few days to prevent damage to the coating.

I bought an aquarium bubbler too, but I doubt it helps any.