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