Every weekend (Friday night around 5/6 through Sunday night) are the busiest times for F&W because that's when all the locals come to the park. The best times are during the week mostly the days without evening EMH.
The "first" day of F&W will most likely be on a Thursday. F&W usually has what they call a cast member preview day, but anyone can purchase items from the booths. This preview is the day before the official opening date, as a rule.