Ours was about 45 minutes, and we had an awesome celebrant who was sneakily writing down everything we said every time we spoke. She'd ring with an innocent enough "question" and engage us in a chat, and then ended up finding out some special little nuances. She built an amazing ceremony around this.
We also submitted a few things that we wanted included, like we wanted soemthing in there about acknowledging the love of ALL couples, and a few other things that we wanted. We also wrote our own vows, and chose our own readings. Our readings were a Pablo Neruda sonnet (I lived in Latin America) and a reading from The Velveteen Rabbit, read by a young cousin.
It is easy to do! Go for it!