Get now Playing gives only the movies that have been released in the theater recently. ( 2 and 3 stand for theatrical release) There is a specific date range that the system itself decides and returns you the results page-wise. Each page has a release date range that you get with the response. You can't query with your own date range.

PS. If you want movies from specific release date range, try /discover/movie where you can sort movies depending on release date

Clear, Thank you!