We did try going there right after lunch and the line was about 45 mins long. If you have enough days in the park, try to do that first thing on one of your mornings.
This week, the park opened at 8 am Fri - Mon, and at 9 am Tue - Thurs. The Entertainment Guide says that Pixie Hollow was from 9 am - 5 pm. Not sure what the schedule will be when you get there, but this will give you an idea.
Pixie Hollow is located in the place that used to be the Meet & Greet for Ariel.......she used to sit in a giant clam shell for pictures. If you are looking at the castle, it is to the right, kind of right up against the backside of the Matterhorn. It's kind of hidden away, so you might have to ask someone.....unless of course you see the line of people!