I Have Been Prescribed Dymista. In The Past Year I

I have been prescribed Dymista. In the past year I have had reactions to antihistamines and Flonase, I believe because I had been exposed to Black mold. I am simply trying the Dymista to see how it will work for me if at all. Do you know how long approximately after the first use how long it works before needing to do the second dose. Is it a 4, 6, 12 or 24 hour drug?