I have trouble parsing the idea of a P0 that takes a quarter, I guess I'm too stuck in Pn as "incident" rather than planned work.
Indelibly etched in my mind is that P0 is like "patient is not breathing" / "everything else is pointless until we fix this".
A "P0" that far out sounds to me like something with a tight (calendar vs estimated effort) deadline and some sort of fairly serious contractual or regulatory penalties for missing it.