They may, and some new grads do change jobs within their first year. But if you've already found one job in the specialty you're interested in, it would be smart to hold it for at least a year.
As a new grad in critical care, after sixth months you will be barely out of orientation. Your unit and hospital will have already invested a lot of money and effort in making you just competent enough to begin solo practice, and leaving them immediately for a new job will be (correctly) perceived as being job-hopping. By both your current and future employers. It will be years before that stops looking bad on your résumé. Imagine years from now, having to still answer questions from hiring managers about why you only lasted six months at your first job- were you incompetent and left in a hurry ahead of a firing? Did you clash with other personalities? Or was it just that you're unreliable? Or worse, not getting a chance to answer the question because they toss your resume without calling you.
And what if you have real problems at your second job that require a hasty exit, or an even better opportunity shows up six months in to that one? You could easily wind up with a resume that's poisonous to your future career. And don't bilk a community hospital that took an expensive chance on you in order to speed your career progression up by a few months.
Life happens and sometimes we have to leave jobs after a shorter time than we hoped, but taking a new grad position with the specific intention of leaving it after six months is exactly the kind of behavior that makes the job market for new grads so hellish. Your plan is the sort of thing that prejudices managers against other new grads.