I do see now that I left out important
information, but you solved it anyway. Your assumption that the
times are in cells as times with colons was correct, and I had
actually overlooked that I had stripped the date information out
intentionally because the data  comes in 2 different forms from 2
different sources. Separating the DATE and time  was a way to make
sure the data was in the same form for analysis.
So, David G.'s point about the original Excel values for dates
and times would have worked, except that I had removed the DATE
part, which I should have mentioned. However, the MOD part of the
formula that David S. directed me to seems to have solved the
problem. I've got to sift through the existing formula in order to
add that in, because I had written in error  traps in the formula
itself, but that shouldn't be hard to figure out.
Thanks again to a great group. You did it again.