My first nursing job was Labor & Delivery. Learned to scrub and circulate C-sections, enjoyed that, and decided to transfer to the OR.
Length of orientation depends on the individual OR - an OR in a Level 1 trauma facility that does hearts, trauma, transplants, etc. will have a longer orientation period than a small community hospital that only offers a few specialities.
One thing to be sure of-- be sure that the OR where you will work offers a structured orientation program. A nurse without OR experience really needs a good orientation, and sadly many OR's have extremely haphazard orientation programs. Some hospitals offer a formal OR nurse course. Many hospitals will require a committment, 6 months to a year, in return for the training.
This link to the AORN (Association of periOperative Registered Nurses) website lists many of the OR courses aroung the country:
The important thing here, as with any job is to be selective.
You are no doubt aware of the nursing shortage--the shortage of OR nurses is even more pronounced, in part, because for many years nursing schools have not offered students any opportunities for OR experience. SO-- you should be able to find a good OR that will welcome you with open arms.