Bring your camera! And dont forget to bring a lens too! Bring everything! And timing??? Well, do it when the sun light is the best. Inless, you have no idea when the sun light is most accomodating and flattering.
Ok, ok. If you have no experience, why are you organising? Why don't you join a shoot or two first, observe what's been done, what to bring, what to do, and when to shoot, then organise your own!
Its almost impossible to tell you what to bring. It's all depended on what kind of outdoor shoot your are planning or thinking of. Do you have any idea?
Best timing would be 7am-10am or 4pm-dark.
And besides bringing all the camera equipment, u would also need to bring some mosquito repellent spray, scotch tape, hair pins, some water, find a place for model to change clothes, find a shelter in case rain.