How to find minimum interval?

[macfuller]

We have a file of order history for supplies. Within a storeroom I would like to find the minimum order time for each item within a selected time period. We run 2-bin Kanban so two orders on the same day would indicate a stockout.

Primary key is Storeroom_Item#_Unit of Measure e.g. ABC123_005678_Box
Data is (simplified):
Primary key Order Date Order Qty

First, I'm trying to think if there's a single measure I could write against the data to get the minimum interval between two dates without a helper column, but I haven't figured it out. It seemed more elegant...

More likely I would create a helper column in either PowerQuery or DAX to provide the interval between dates and then just do a MIN([Interval]) expression. I prefer to use PowerQuery but I think I'd have to do a self-merge, but the files are big and I don't want to slow down the already-lengthy daily refresh process. Off the top of my head a DAX calculated column would probably be something along the lines of

=EARLIER([Order Date]) - CALCULATE(MAX[Order Date], FILTER(Orders, EARLIER([Primary key] = [Primary key] && EARLIER([Order Date]) > [Order Date]))

plus some condition to apply a blank value if the record is the first order within the time period. (Would I have to copy the whole CALCULATE segment into a wraparound IF statement?)

That's why I'm hoping for something prettier!

 

[macfuller]

The actual DAX for the interval column (I welcome cleanup suggestions!) is

=
IF (
    ISBLANK (
        CALCULATE (
            COUNTROWS ( 'Order History' ),
            FILTER (
                'Order History',
                EARLIER ( 'Order History'[FK_CartItem] ) = 'Order History'[FK_CartItem]
                    && EARLIER ( 'Order History'[Demand Date] ) > 'Order History'[Demand Date]
            )
        )
    ),
    BLANK (),
    FORMAT (
        'Order History'[Demand Date]
            - CALCULATE (
                MAX ( 'Order History'[Demand Date] ),
                FILTER (
                    'Order History',
                    EARLIER ( 'Order History'[FK_CartItem] ) = 'Order History'[FK_CartItem]
                        && EARLIER ( 'Order History'[Demand Date] ) > 'Order History'[Demand Date]
                )
            ),
        "###"
    )
)

Yes, I'm stuck with Office 2013 at work so no DATEDIFF.