Here is a query that will display the Average Days to Pay against a BPCode:-
SELECT
T4.CardCode, (SUM(DateDiff(DD, T4.DocDate, T1.DocDate))/COUNT(T4.DocNum)) AS 'AVG. Days to Pay'
FROM OCRD T0
INNER JOIN ORCT T1
ON T0.CardCode = T1.CardCode
INNER JOIN RCT2 T3
ON T3.DocNum = T1.DocNum
INNER JOIN OINV T4
ON T4.DocEntry = T3.DocEntry
AND T3.InvType = '13'
GROUP BY T4.CardCode
ORDER BY 'AVG. Days to Pay' DESC
Many thanks
Alan