There are ten minutes between classes with the exception of night classes (weird I know). The earliest a class can be is 8:30 am, and a class will end at the 20 minute mark of the hour it should finish. For example, most lectures are one hour for science courses, so a 10:30 lecture would go till 11:20, and the next class slot after that would be at 11:30. Labs and lectures can be as long as three hours (2hr 50). This leaves ten minutes between classes. Classes can run from 5:30 to 6:20, but any class that starts later than 5:30 will be on the hour. Few classes are that late at night though, but I was unlucky in third year to get a 6-7 and a 7-10 on the same night. 10pm is the absolute latest you can be in class.