JM
VAR CurrentDate = [Order Date]
VAR CurrCustomers = [CustomerKey]
VAR PrevDate =
MAXX(
FILTER(
ALL(
Sales[Order Date],
Sales[CustomerKey]
),
Sales[Order Date]<CurrentDate&&
[CustomerKey]=CurrCustomers
),
Sales[Order Date]
)
RETURN
DATEDIFF(PrevDate,CurrentDate,DAY)