This may sound really stupid, but I registered for the exam in July 2014 by paying through credit card and kept postponing it. Right now I am busy with other stuff and want to know the maximum time within which I need to take the exam.
When I saw this, my first thought was "I"m not sure." I see you haven't gotten a reply which implies others aren't either. I think your best bet is to log into PearsonVUE and see how far out it lets you reschedule. And then post back here with the answer so that we know.
As far as I know there's no limitation on rescheduling. And based on the Reschedule Policy of the Oracle Certification Program Policies there's just 1 restriction: you must reschedule at least 1 business day prior to your exam appointment. You could even cancel your exam. According to the Cancellation Policy you lose your exam fee only on a no-show or a cancellation less than 24 hours before your exam appointment.