When arriving in Milan, approximately how long does it take to get through customs?
The answer depends on a lot of factors (e.g. day/time of arrival, staffing, etc.). We travelled through Milan Malpensa twice and don't remember it taking more than 20 minutes or so.
Customs, no time at all unless you have something to declare.
Passport Control, depends on how close you are to the front of the plane and therefore the front of the line, and how many flights arrive along with yours. Count on an hour and hope it is better.
Once through Passport Control, claim your luggage then walk out through the "Nothing to Declare" doors unless you have something to declare.