Have you ever tried to schedule a field study while you're teaching? If so, you know it's practically impossible because you simply don't have any wait time during working hours when you teach children.
Hence, I recommend that you try to schedule field studies during the lazy days of summer. Typically the docents and schedulers have the time now to talk.
Bringing our students to wonderful places of learning is an important part of the learning experience, and summer is a good time to schedule those events.