午前 0 時 (00) の軍事時間である DATEPART 時間を、計算に必要なときに使用できる値に変換する方法を教えてください。

何も不足していない場合は、ループの代わりにこれを試すことができます:

DECLARE
  @StartTime time,
  @EndTime   time;

SET @StartTime = '22:30:00';
SET @EndTime   = '00:52:00';

WITH timerange AS (
  SELECT
    StartTime = CAST(@StartTime AS datetime),
    EndTime   = DATEADD(
      DAY,
      CASE WHEN @StartTime > @EndTime THEN 1 ELSE 0 END,
      CAST(@EndTime AS datetime)
    )
),
hourly AS (
  SELECT
    n.number,
    t.StartTime,
    t.EndTime,
    HStart = DATEADD(HOUR, DATEDIFF(HOUR, 0, t.StartTime) + n.number    , 0),
    HEnd   = DATEADD(HOUR, DATEDIFF(HOUR, 0, t.StartTime) + n.number + 1, 0)
  FROM timerange t
    INNER JOIN master..spt_values n
      ON n.number BETWEEN 0 AND DATEDIFF(HOUR, t.StartTime, t.EndTime)
  WHERE n.type = 'P'
),
hourly2 AS (
  SELECT
    number,
    HStart = CASE WHEN StartTime > HStart THEN StartTime ELSE HStart END,
    HEnd   = CASE WHEN EndTime   < HEnd   THEN EndTime   ELSE HEnd   END
  FROM hourly
)
SELECT
  StartHour   = DATEPART(HOUR  , HStart),
  StartMinute = DATEPART(MINUTE, HStart),
  EndHour     = DATEPART(HOUR  , HEnd  ),
  EndMinute   = DATEPART(MINUTE, HEnd  ),
  StartTime   = CAST(HStart AS time),
  EndTime     = CAST(HEnd   AS time)
FROM hourly2
ORDER BY number
;

生成される出力は次のとおりです:

StartHour   StartMinute EndHour     EndMinute   StartTime        EndTime
----------- ----------- ----------- ----------- ---------------- ----------------
22          30          23          0           22:30:00.0000000 23:00:00.0000000
23          0           0           0           23:00:00.0000000 00:00:00.0000000
0           0           0           52          00:00:00.0000000 00:52:00.0000000