Does oil-based polyurethane have any residual toxicity past setting?
There are many discussions on this to be found. The bottom line is that any product has a parabolic curve of off-gassing over time. It reaches extremely small quantities after a few days of suitable curing conditions, and is almost at zero after a few weeks. Very few people would detect substantial odor after that. 

I finished my office desktop with oil-based poly last fall. It was cured for long-term contact after about 2 days, but I could smell it for a few weeks. I don't notice it anymore a few months later. Your mileage may vary and depends largely on your personal definition of "toxicity".