Are you sure you're last digits are milliseconds (thousandths a second)
or are they hundredths of a second?

If the latter:

B1: =LEFT(A1,8)+LEFT(A2,8)+(RIGHT(A1,2)+RIGHT(A2,2))/8640000

if you format the result as hh:mm:ss.00 will return 00:10:30.76.

The average:

B2: =B1/2


In article ,
"JD" wrote:

I'm trying to work with time. I'll be adding and averaging many different
process times for a business project. How do I format these times and write
a formula. The tricky part is the times are all the way to milliseconds.
The format is 00:00:00:00 in hh:mm:ss:ms. Say I have 00:05:55:78 and
00:04:34:98. How do I add these and then also get an average of the two??
I've been stuck with this problem for a while. Version 2003 Excel.