Best advice I've ever been given "The only break you need is the fact that you got a break when you got the job". . . It's hard times to be hard pressed about getting paid extra money to work extra hours. Buck up, tough up, grow to expect it and make it a normal. It helps you deal with the fact that the hours are longer, but you come to ease into it as you expect it.
Labor laws are not there to protect you in this area - Sorry hard truth. I've been forced to stay over an extra 4 hours on a 12 hour shift numerous times, heck even volunteered other times. 16 hours makes for a long day, however, anything over 16 hours does fall into a dangerous territory for Legal since insurence no longer provides workmens coverage if they are on site for more than 16 consecutive hours. Most places that have workmans comp insurance in place must follow these standards. 16 on, followed by a min of 8 off before you can return to work.
Welcome to the real working persons world.