I have two machines in a high school in pa.  I use Royal machines that have built in timers for vending.  You can even choose which selections can vend at which times.  For instance...I let water vend all day...but any beverage over 50 calories has to vend a half hour after the school day.  One of my machines vends Coke zero products all day.  The kids really like Vanilla Coke Zero and Cherry Coke Zero.  I also vend Propel and Powerade Zero.  All newer G3s and Merlin 4's should have the timer op