Question about express

I’m confused. I have seperate theme park admission already that allows me to park up between the two orignal parks and one day at epic. (4 day original + 1 day at epic and then a seperate one day at epic in the middle) Can I use this express pass at both universal studios and islands of adventure the same day? Or is it one park per day? Also I bought an extra day at epic in the middle of my five day ticket. Could I theoretically use this in the middle and do my one day at epic, one day park hopping between the two orignal, and then my second day at epic? This is getting complicated LOL