I had an EUA (exam under anesthesia) done at CC in June - I had a fistula as shown on an MRI. It was about 1-1/2 years old. Anyhoo - a seton was placed in hopes of healing it eventually and possible surgery down the road.
The EUA itself took only about 40 min., maybe a bit less. They treat the process like they would surgery: pre-surgical prep, the surgery itself, post surgery recovery, etc. Other than fasting, there is NO PREP - no enemas, etc.
I got there around 8 am, finished around 3 pm. Went home (3 hr. drive drive) and was fine. I'm not sure how long a drive you have, but you might want to take a pillow (or doughnut cushion) with you, depending on the location of your fistula (mine was pouch-vaginal). I had it done on a Fri. and was back to work on Monday, if I recall correctly. They gave me pain killers, I forget which ones (sorry!), but only took one and needed no more.
Good luck, and let us know how it goes!