Also curious as to how different this query would be from yours
SELECT
p.PRON,
a1.TimeStamp,
c.[Current Proc Point],
a1.ProcPointStartDate,
Nz(a1.EndDate, Date()) AS EndDate,
Int(Nz(a1.EndDate, Date()) - a1.ProcPointStartDate) AS TimeInProc,
a1.[Updated By],
c.PALT
FROM (...