Games can vary in time depending on which mode you are playing. The standard set time for each half is set to 6 minutes. However in offline game modes where you are playing against the AI and not on ultimate team you can change this to play anywhere from 4 minutes per half all the way to 20 minutes per half.
Although I can say that even though 20 minutes per half might sound a good idea. It’s incredibly boring unless you’re playing offline against your mate. Then it can be quite good when you’re thrashing him 25-0.
Online games, and this includes all of the following game modes. FUT, Pro Clubs, and online seasons. They are set and restricted to 6 minutes per half.
6 minutes gives you and your opposition a good enough amount of time to score goals and make a decent game without it feeling to long or to short.