How soon to shower after drops?

 As a newbie here I hope you will forgive me if this question has already been addressed. I have been using a variety of prescribed drops to reduce my IOP and of late seem to have  eye irritation no matter which drop. Right now I am on Xalacom, a drop in each eye once a day in the morning. The doc told me the irritation is more from the preservative than the medicine itself. I was wondering if after instilling the drops, if I waited a decent time for the drops to absorb and then washed my face/eyes then perhaps that would get rid of the preservative residue if any in my eyes.