When a job is initially generated, it is given a status of New and a planned start and finish date derived from its parent item’s Lead Days and Job Days settings.  Manual rescheduling of New status job dates is not permitted prior to job release because doing so would disrupt the inter-connected date relationships that comprise the master schedule.  

Instead, job rescheduling is done automatically when material availability enables jobs to be released to production in the Job Control Panel.  If the actual release date differs from the planned start date, the job finish date is rescheduled to update the master schedule with a realistic supply date.