Lots of ways!

You could still use a potentiometer, and read it with an ADC in the microcontroller;

You could use a multi-position rotary switch, or multiple buttons to select the required delay from a range of options;

You could use 2 buttons - one to increase the time, one to decrease it;

You could use a keypad and enter it directly;

You could use one of those "jog wheel" thingies that are so popular these days;

You could get really sexy, and use one of these:
http://www.qprox.com/products/qslide_qt401.php
http://www.qprox.com/products/qwheel_qt510.php

etc, etc, etc,...


You still have the issue of feedback - how do you confirm that the dispenser is dispensing at the correct rate