MrEyes,

Excel reads time as decimal values, so the multiple decimals are throwing it off. Once you tell Excel how to read your data you'll be fine. I'm assuming

part1.part2.part3

translates to

hour.minute.second

If so, use this formula:

=TIME(LEFT(B1,2),MID(B1,4,2),RIGHT(B1,2))-TIME(LEFT(A1,2),MID(A1,4,2),RIGHT(A1,2))

Basically it takes the value in each cell, cuts it up into pieces, and tells Excel that the first two characters are the HOUR, the two characters in the middle are the MINUTE, and the right two characters are the SECOND.

Knightly