Summarize start and end durations by 30 minute interval

WITH cteTimeSlots (SlotStart, SlotEnd) As
(
    SELECT
        Convert(time, '00:00'),
        Convert(time, '00:30')
    
    UNION ALL
    
    SELECT
        DateAdd(minute, 30, SlotStart),
        DateAdd(minute, 30, SlotEnd)
    FROM
        cteTimeSlots
    WHERE
        SlotStart < '23:30'
)
SELECT
    S.Date,
    S.FIRSTNAME,
    S.LASTNAME,
    S.ID,
    S.ACTIVITY,
    T.SlotStart,
    T.SlotEnd,
    DateDiff(minute, GREATEST(T.SlotStart, S.START_EST), LEAST(T.SlotEnd, S.END_EST)) As Duration
FROM
    #TMPSHRINK As S
    INNER JOIN cteTimeSlots As T
    ON T.SlotEnd > S.START_EST
    AND T.SlotStart < S.END_EST
;

DateDiff(minute, CASE WHEN T.SlotStart > S.START_EST THEN T.SlotStart ELSE S.START_EST END, CASE WHEN T.SlotEnd < S.END_EST THEN T.SlotEnd ELSE S.END_EST END) As Duration