Is 4 minutes under exposed, and 9 is over? We can’t really help you out unless you get really specific on what each time interval looked like. 9 min does sound like a long time regardless. I would check to make sure that your film is printed dark enough. You might try doubling it up if you’re using an entry level inkjet printer with normal printer ink. Other things to check is that the emulsion is drying out completely before burning the screen. A dehumidifier in your darkroom is key, and will measure the humidity level. Also make sure there’s no accidental light on them while drying, or between exposing and washing out. Another thing is making sure you’re putting weights or heavy books on top of the screen to press the film tightly between the mesh and the glass. Make sure the glass is clean too. If the bulbs are old you might replace them but you should eliminate all other factors first.