I did wonder about STUFF, e.g.

SELECT STUFF ('200', 2 , 0, ':')

DECLARE @MJBtime INT

SET @MJBtime = '10200'

SELECT LEN(@MJBtime)

SELECT STUFF (@MJBtime, LEN(@MJBtime)-1, 0, ':')--Not 2 as 1st value before first character

SELECT STUFF(STUFF (@MJBtime, LEN(@MJBtime)-1, 0, ':'),LEN(@MJBtime)-3,0,':')