Commute time is 10 minutes between your two terminals and that's not counting the waiting on the bus time. I would figure it's a minimum of 30 minutes in real world.
So… you have to get off the plane, through immigration and pick up your luggage. Even if you are in in F assume this will take a minimum of hour based on my experience at MAD flying in Business. (plus your friend is in Y..so….) It's pretty busy there in the morning. Then 30 minutes to connect over to 4 (The bus is never there and the 10 minutes the airport suggests seems optimistic to me, that shuttle was a nightmare). I think you are looking at 2 hours to get to T4.
Good Luck