After allowing the first coat of epoxy to cure for 24 hours, the application of subsequent coats of Pond Shield can be done as each coat tacks up. This means that you can get multiple coats done in one day. Sand the first coat with 60-grit sandpaper.
The fiberglass can also be sanded and smoothed out to give a more finished look.
Bear in mind that you should be applying each coat very thin. The idea is to build the coating up while locking off and gaps in the grain of the wood. The first coat of Pond Shield should have done most of that work, but as is with wood, any liquid tends to make the grain swell slightly at which point small gaps form that are being filled with each coat.
Apply the epoxy coating over the top of the tank edge as well. Later when the cap is coated and put in place, this will keep water from seeping into the seam and swelling the wood there.