3 minute switch/timer
An alternative would be to use a time delay relay designed for industrial control systems, such as this 820 Series from Magnecraft.  This relay could be set in 'inteval mode" and installed in series with an existing toggle switch (on the load side).  Then you would just turn the mixer on, and the relay will limit the run time of the mixer to the programmed time.  turninh the power switch off and on again would initiate a new cycle.  Turning off the switch will immediately stop the cycle.