Try this
SELECT CONVERT(char,DATEADD(mi, mindatafld, '1/1/1970'),108)
unless goes over 12 hours.
Also you might need to do something like this
SELECT CAST(mindatafld / 60 as varchar(5)) + ':' + CAST(mindatafld % 60 as varchar(5)) + ':00'
of course you will need to fix the minute position if not 2 characters in length, I didn't go into that.
Probably can come up with at least one other way, but it is late and I am fried.