I cleaned the bottle, put a cork in the top of it, and started brushing on the mold builder.
The very first coat I let dry for about 3 or 4 hours. I could tell that it was really good and dry. It wasn't squishy or sticky at all, so I felt ok with putting the second coat on. Then I went to bed and let it dry overnight.
The mold builder turns kinda like a clear yellowish color when it's dry. When I see that, I kinda touch it to make sure it feels dry, then apply the next coat. I have a little space heater that I sat on the table next to the mold to help it dry. I'm probably just wasting electricity though because it really doesn't take very long for it to dry at all. You'll be able to tell when it's ok for the next coat.
After a layer would dry, I would check over the bottle to see if there were any spots that looked thinner than the rest of it, and dabbed a little mold builder on it, then let it dry. I did that because I was afraid of it being a weak spot in the mold. Once that was dry, I just brushed on another layer all over it. Don't worry, you will be able to tell when it's good and dry and ready for the next layer. It changes color and it's not sticky to touch.
This is the bottle after 11 layers of mold builder brushed on it. It's dry in this pic.