Was there on July 8th of this year. Go when it opens and you'll have the run of the place - and it opens at 10:00, which isn't too early. A ton of butterflies - unlike some zoo/greenhouse exhibits you see, they birth butterflies year round in the conservatory, so there's no shortage. My 6 year old daughter loved the fact they landed all over her. Wear something colorful. Good time.
Have you considered the WEGO people mover system? Depending on your location and plans, you might be able to make a wash - or do better than paying for parking. Especially if there's just two of you.