Leaving first job (trading) after only a few months?

Long story short, I'm a new analyst on an S&T desk, and I honestly hate it. I know it's only been a short time, but I find the work very non intellectually stimulating and know that the future of S&T is generally shrinking. I've also developed some health issues over the past year that are not super compatible with the higher-than-average working hours and general S&T lifestyle. Additionally, I feel somewhat misled, because I was told that the role would be more quantitative/interesting in other ways which it is not. I graduated from a top target with a quantitative major, and also was admitted to our 5th year master's program (which I have deferred for now). I know that staying under a year usually doesn't look great, so just how bad would it be if I either switched to a different job or went back to school for the master's starting next semester? And when seeking new jobs, would the reasons I listed above be seen as valid enough for quitting so soon?