Try:

=TIME(MID(A1,10,2),MID(A1,12,2),0)-$C$3

"Terry Pinnell" wrote:

I'm struggling with this one and would appreciate some help please. I
have a Start Time fixed in C3, 10:20, in Custom format hh:mm. IOW,
getting on for half past ten in the morning. In the body of the
worksheet I have

Col A Col B
Filename Time from Start
----------------------------------- ---------------
20050813-105501-KennetAvonJoins.JPG
20050813-112231-ReadingHenley.JPG
20050813-114837-Sonning Lock.JPG
etc

Each filename is prefixed with date and time, e.g.
20050813-105501 is about 10:55 on 13th August 2005 (I'm ignoring
seconds).

I want to calculate and enter the times from start in Col B, like
this:

Col A Col B
Filename Time from Start
----------------------------------- ---------------
20050813-105501-KennetAvonJoins.JPG 0:35
20050813-112231-ReadingHenley.JPG 1:02
20050813-114837-Sonning Lock.JPG 1:46
etc etc

Could someone help me derive the correct formula please?

--
Terry, West Sussex, UK