DECLARE @t1 DATETIME = '2014-05-02 10:30:43';

DECLARE @t2 DATETIME = '2014-05-02 14:25:13';

-- Show the time difference in HH:MM:SS (assumes timespan < 24 hours)

PRINT CONVERT(CHAR(8), @t2 - @t1, 8)

-- Shrink to HH:MM - value is truncated, not rounded to nearest minute

PRINT CONVERT(CHAR(5), @t2 - @t1, 8)

-- Round the minutes by adding 30 seconds

PRINT CONVERT(CHAR(5), DATEADD(SECOND, 30, @t2 - @t1), 8)

-- Casting the timespan to TIME allows using CAST(time AS CHAR) instead of CONVERT(CHAR, datetime, 8)

PRINT CAST(CAST(DATEADD(SECOND, 30, @t2 - @t1) AS TIME) AS CHAR(5))

-- Handle timespans over 24 hours as HHH:MM ( up to about 68 years )

-- Using DATEDIFF(MINUTE, @t1, @t2) will also run into rounding issues, so use seconds and add 30

DECLARE @mins INT = (DATEDIFF(SECOND, @t1, @t2) + 30) / 60;

PRINT CASE WHEN @mins < 600 THEN '0' ELSE '' END + LTRIM(@mins / 60) + ':' + LTRIM(@mins % 60)