Hi Davi,
Glad to hear that you are interesting in contributing, please sign http://www.jboss.org/contributor first, and Alejandro will reply you later. As you see, he is the Chief. :)
And for CRON, I just find ther is an org.jbpm.pvm.internal.cal.CronExpression in the trunk. Not sure how to use it. I think I should do some test for it. If I got any result, I will reply here.