They advertised a night shift position, and you applied for and were offered a night shift position. Is it any surprise that they don't want to switch you to days ASAP? State facilities tend to have long probationary periods because, in most states, becoming a permanent state employee (after successfully completing the probationary period) is a big deal
-- it's like getting tenure, you basically can't lose your job unless you do something really, really bad, on purpose.
And state agencies are typically considered very good, desirable employers
IMO, if you know you're going to screw them over the first chance you get (quit for another job), don't, as you put it, waste your time and theirs. There are lots of folks who would be v. happy to get that job, and would be happy to settle in and stay.