Average is from 9:00 am to 5:30 pm. Go to the client office and work with the audit teams on various work-papers that they need assistance with. Involves basic auditing work and training and miscellaneous office work. Much of it is learning and watching training videos and then learning as much as you can with paperwork.
The day in the life of an assurance summer intern varies. After the first week of training (in the Orange County office), interns will be placed on a specific engagement team (a client to service). They may or may not be placed with other interns on the same team. If the intern has a car, BDO may ask you to commute to the client sight. Once on the engagement, day-to-day life is fairly 9:00am - 5:00pm, learning and communicating with the team you are on. Microsoft Excel is used for the majority of the day, and typical tasks are along the lines of reconciling a clients' 10-K to bank statements, and checking for accuracy on certain documents.
The biggest takeaway from my intern days is simply a better understanding of how to handle myself in the workplace. More important than the work itself, is creating a solid relationship with other interns, colleagues, managers, and partners. BDO does a great job of both assigning challenging tasks to interns, and fostering an environment where interns can grow into professionals.