No. Mess food is served only at specified times. In most hostels, it is 7-9 am for breakfast, 12-2pm for lunch and 7-9pm for dinner. Some hostels do serve snacks and tea in the evening. However, most hostels have shops right outside if you want something to munch on and there are plenty of food outlets in and around the campus for a quick bite. Some hostels have night messing facilities too.