Add Date Only To Time Only = Datetime ?

I have a field that contains only a date, and a field that only contains times. If I try to add the two together, I get some meaningless date like year 2111.

The raw data looks like this
EVT_DT='2005-12-05 00:00:00'
EVT_TM='2005-12-06 13:59:00' //today's date

I wrote a function that gives me the minutes past midnight for the EVT_TM
and use a dateadd(n,myMinutesFuntion(EVT_TM),EVT_DT), but it kills the performance in the nexted cursor.

Thanks,
Carl