How Long Does Vistamethasone For Blocked Nose Take To Show Effects?

Hi I have been told to use vistamethasone 2drops in each nostril twice a day. This is because my nose is always blocked. For the last few years I have been using vicks sinex which I have been told to stop. My problem is as soon as I stop I won t be able to breath through my nose until the vistamethasone starts working which iv read can take upto a week or two... im going to be in big trouble.