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
Build every hour, weekends in April and December: H * * 4,12 *
Build at 8.30am on July 4: 30 8 4 7 *
Also: @hourly, @daily, @weekly, @monthly, @midnight
Jenkins build periodically