Calculating time difference before and after a specific time

// Assuming you have a table
// with columns Datetime and Machine.
// When you select a machine,
// you want to know the diff
// between the two closest times
// to 6am, one before and one after it.
// If more than 1 machine is selected,
// BLANK should be returned. Bear in
// mind that the measure honours all
// the currently set filters.
// Let the table be T.

[Diff (min)] =
var __onlyOneMachineVisible = HASONEVALUE( T[Machine] )
var __minDate = INT( MIN( T[Datetime] ) )
var __maxDate = INT( MAX( T[Datetime] ) )
var __onlyOneDayVisible = ( __minDate = __maxDate )
var __canCalculate = true()
    && __onlyOneMachineVisible
    && __onlyOneDayVisible
var __output =
    if( __canCalculate,
        
        var __closestBefore6am =
            CALCULATE(
                MAX( T[Datetime] ),
                KEEPFILTERS(
                    // We make use of the fact
                    // that one can compare datetimes
                    // with real numbers since a date
                    // under the hood is a real number,
                    // where the integer part stands for
                    // the day and the fractional part
                    // stands for the hour.
                    T[Datetime] <= __minDate + .25
                )
            )
        var __closestAfter6am =
            CALCULATE(
                MIN( T[Datetime] ),
                KEEPFILTERS(
                    T[Datetime] > __minDate + .25
                )
            )
        var __shouldCalculate =
            and(
                not ISBLANK( __closestBefore6am ),
                not ISBLANK( __closestAfter6am )
            )
        var __diff =
            if( __shouldCalculate,
                DATEDIFF( 
                    __closestBefore6am,
                    __closestAfter6am,
                    MINUTE
                )
            )
        return
            __diff
    )
return
    __output