Let users work with software 30 minutes. Reluctant users may be engaged by shorter work periods and more frequent instruction periods. Users can often teach other users about the software.
Users teaching others is a good way to extend learning.
Three 40 minute sessions would be minimum for engaged users. Apply Hold a SimFarm contest. Single users, or teams of up to 4, work to build a farm for 60 to 90 minutes. Visit a farm implement store. Have the users price out tractors, combines, and other equipment from SimFarm.