Yes, some smaller hospitals require nurses to work pre-op holding and PACU in addition to OR.
Some large hospitals have night shifts in the OR- this is generally at hospitals with trauma centers.
As far as flexibility of working hours- in general the larger the hospital, the more flexibility is offered. In addition to 7 -3, many hospitals offer 3 - 11, 10:30A - 7P, 3 - 12 hour shifts, 4 - 10 hour shifts, part-time and flexipool.
Regarding roles: a registered nurse can perform any of the duties that an OR tech can perform.
Depending on the facility, only RN's circulate and perform patient assessments. The OR tech functions under the direction of a registered nurse. There are hospitals where techs circulate, and an RN is responsible for 2 or more rooms, but I have never worked at one one of these facilities.
Some hospitals RNs scrub and circulate, some hospitals RNs only circulate, and techs do all the scrubbing--this is because hospital administrators see this as a way to save money, as techs make less than RNs.
You should gain a lot of useful information in your tech program- sterile technique, understanding of the procedures, instrumentation, etc. If you decide to stay in the OR after you finish nursing school you will have a good base of knowledge to build on. A circulator who knows how to scrub is a better circulator, and a scrub who knows how to circulate is a better scrub.