Currently, the Cron expression in the Schedule section of Feed Summary provides no clue for what constitutes a valid expression. This is especially troublesome since there are multiple formats for cron including, but not limited to: Quartz Cron, Linux Crontab.
We should put an incon near the cron expression field that will popup a summary for help. e.g.
Cron Expression docs can be found at: http://www.quartz-scheduler.org/api/2.1.7/org/quartz/CronExpression.html
Perhaps a Summary of Options with a external link to the Java Docs for CronExpression would be sufficient. Here's a summary taken from java docs: