Taking antibiotics when you have a bacterial sinus infection will make the sinus infection go away much sooner.
If you have a bacterial sinus infection and the doctor prescribes you some antibiotics the antibiotics should begin working on killing the bacteria that is causing the sinus infection within a day or two.
Then after around 4 to 5 days of taking the antibiotics the sinus infection should go away fully and you should be feeling better.
You should continue to take the antibiotics as long as the doctor says you should even if you're feeling better as taking the antibiotics will help keep new bacteria from growing inside your body so you won't get reinfected with the bacterial sinus infection soon after it's going away.
When you do have a sinus infection you should also stay hydrated by drinking plenty of water or juice that contains Vitamin C such as Orange Juice, use a humidifier and take a steamy shower or use a humidifier to keep humidity in your bedroom or home.