How long should I stay at the job?

I started my new RN job at a small community hospital since Jan 2015. I'm a new RN but has worked as a LPN in the same hospital for over three years. My training was short three weeks but the transition was easy because the only tasks I did not do as a LPN are blood admin, IV push meds and drips.

I do like my current job. My boss and coworkers are great. I am learning about cardiac drips, post-cath and CVA pt care. However, I don't feel I'm learning that much at this job. Our ratio is increased to 5:1( cardiac step down) and all I do is to run around and try to get my tasks down. I had no time to look into pt's hx, patho, meds, etc. In addition, my dream job is ICU in another large hospital. The manager told me she will only hire me if I had worked in their step-down for a year.

Just wondering what is appropriate time frame to stay at this job... six months? A year? thanks for any input.
A year is better