From answers.com:
It depends on the recipe that your making, but just raw vegetables (add water) should cook on high within 2 hours once they get to the boiling point. On low, it would be maybe 3 to 4 hours. Dried beans take about 5 to 6 hours on high, or you can put them on low and cook all night and the next day until they are as done as you like them to be.
Source: http://www.answers.com/Q/How_long_do_you_cook_vegetables_in_a_crock_pot