how many hours does it take to see Epcot with 2 45+ adults ?

You should plan for a whole day to do it at your own pace

Epcot is divided into a futuristic part with rides and a part that consists of different country representations. If you are into both of these then all day is appropriate. If not then maybe just half your day.

There is a lot to do and see. Ive been there for 12 hours and still missed out on some things. Best to get an idea of what countries you want to visit, what shows you may want to see (some countries have small shows in front to watch like drummers in Japan, stunt guys ans singers in Italy and China), and what rides you want to go on. I recommend soarin which can be a 2 hour wait itself. If you want to eat at one of the sit down restaurants you'll want a couple hours to enjoy that. The shops are awesome too. You can make this a 2 day trip and still have things you didn't see.