Hola.
Proba si te sirve de este modo:
Código SQL
[-]
SELECT DATEDIFF(MINUTE FROM CAMPO_1 TO CAMPO_2) AS LAPSO_1,
DATEDIFF(MINUTE FROM CAMPO_3 TO CAMPO_4) AS LAPSO_2,
DATEDIFF(MINUTE FROM CAMPO_1 TO CAMPO_2) +
DATEDIFF(MINUTE FROM CAMPO_3 TO CAMPO_4) AS LAPSO_TOTAL,
...
FROM FROM TU_TABLA
...
Saludos.