Build every hour: H * * * *
Build every 20 minutes: H/20 * * * *
Build every 20 minutes 2am to 11pm: H/20 5-23 * * *
Build every 20 minutes, work time/days (8am-6pm, MON-FRI) only: H/20 8-18 * * 1-5
Build every hour MON-WED and FRI only: H * * * 1-3,5