Unstable?

How long do I have to work at a drowning facility or any facility, to not be considered, an "unstable worker" 1-2 years, 3 years, how long to show that I gave it my all?
I think a year is the minimum, optimally. However, it is never wrong to leave unsafe circumstances prematurely. If you truly feel that your patients are at risk or that your care is substandard and mistakes may be made due to working conditions or lack of resources, then most people would advise you to take your license and run. Someone's career can always survive one blip in their employment history. Take the lessons you have now learned and use them to evaluate any future employers. You likely know much more about what signs to look for in your future interview/shadow experiences.