I have been advised by my doctor to use the rinse to clear my stuffy head due to sinus infection. I want to rinse 4 times today. How many hours should

There is no absolute waiting period between rinsing so you may have to find the best schedule through trial and error. If you find rinsing four times a day beneficial, try doing it every four hours, making sure your last rinse is an hour before bedtime (to avoid residual solution dripping in your throat when you lie down). Do not rinse if your nasal passage is completely blocked, but it is safe if you have some air passing through each nostril. And be careful to blow your nose gently after rinsing to avoid putting pressure on your eardrums.