I've prepared my (sealed wood) pattern today for the Unimold system, and tomorrow will attempt to go through the process for the first time.

Not really. As long as you don't leave it more than 24hrs between stages you will still get a chemical bond between the resin systems. The Gelcoat and Coupling coats will still be tacky (by tacky I mean not cured) after that time as they require the resin from the next stage to cure them, ie the Gelcoat needs the Coupling Coat and the Coupling Coat needs the the Backing Resin. They are all designed to work together. Again hope that makes sense.