Create multiple measures to count alarms in various time buckets

Match =
VAR b =  // starting second for the selected 15 minute bucket of the selected day
    ROUNDDOWN (
        ( MAX ( 'Time Buckets'[Column1] ) + MAX ( 'Calendar'[Date] ) ) * 86400,
        0
    )
VAR b2 = // all seconds for the selected 15 minute bucket of the selected day
    GENERATESERIES ( b, b + 899 )
VAR a =
    ADDCOLUMNS (
        'Table',
        "m",
            COUNTROWS (
                INTERSECT (
                    b2, //  all seconds in the bucket
                    GENERATESERIES ( // all seconds in the alarm
                        ROUNDDOWN ( [Set] * 86400, 0 ),
                        ROUNDDOWN ( [Reset] * 86400 - 1, 0 )
                    )
                )
            )
    )
RETURN
    SUMX ( a, [m] ) // how many seconds in the bucket match the seconds in the alarm

There's not really much to it. Datetime values can be divided into the Integer part (day) and the fraction part (time).  For easier calculation and to avoid rounding errors all values are multiplied by 86400 (the number of seconds in a day) which then results in simpler integer math.

INTERSECT does most of the work by matching seconds between the two intervals.