Assuming you're using a TIME field to store your values, you can use a Tally table and the built-in DATEADD/DATEDIFF functions for this:

DECLARE @t TABLE

(OfficeId INT, WeekdayId INT, StartTime TIME, EndTime TIME)

INSERT INTO @t

SELECT 1, 2, '14:30', '16:30'

UNION ALL SELECT 1, 3, '16:00', '18:00'

;WITH Tally (n) AS (

SELECT TOP 100 30*(ROW_NUMBER() OVER (ORDER BY (SELECT NULL))-1)

FROM sys.all_columns)

SELECT OfficeID, WeekdayID

,TSStart=DATEADD(minute, n, StartTime)

,TSEnd=DATEADD(minute, n + 30, StartTime)

,Timeslot=CONVERT(VARCHAR(100), DATEADD(minute, n, StartTime), 0) + ' - ' +

CONVERT(VARCHAR(100), DATEADD(minute, n + 30, StartTime), 0)

FROM @t

CROSS APPLY (

SELECT n

FROM Tally

WHERE n BETWEEN 0 AND DATEDIFF(minute, StartTime, DATEADD(minute, -30, EndTime))) a

ORDER BY OfficeID, WeekdayID, TSStart