Can a non functional pituitary tumor go away on its own without treatment or any intervention?if yes, can it happen in a year or how long can it take?

No it is unlikely to: nonfunctional pituitary adenomas are generally benign and are quit common as up to 10% of the population may have one. Generally they are benign but if the size increases over time it may result in compression of local structures most concerning of which is the optic chiasm. There is no timeline but may take years to grow large. Generally no treatment is needed unless they enlarge enough >1cm