Answer
Don't use a SYSDATE-based arithmetic expression for a fixed recurring interval like this — instead, keep the schedule type as Custom, but set the Expression itself to an iCal-style recurrence rule, like FREQ=WEEKLY INTERVAL=2 for 'every 14 days.' This recurrence-rule syntax correctly respects the Start Date you've set (including its time), unlike a SYSDATE+N arithmetic expression, which calculates relative to whenever the record itself was last saved rather than the intended start date.