how can I have ruler seconds not start at very start but at the left locator of the project?
??
Because simple arithmetic by the user is quicker and cheaper than six months programming for something only you will use?
You can add an offset for the seconds ruler in Project Setup, but there’s no way specifically to have the left locator be (and remain) at 0:00.
(edit- Buchanan posted while I was typing - didn’t see his post till mine was done)
… although I would love to have separate offsets available for each custom Ruler Track 
.
speak only for yourself if you won’t use it. because all the people i work with would definitely would use it. and it definitely wouldnt take 6 months of programing
All the people I work with just do it. Simple math, no messing with the program. Put a marker on it/them and go. No program to blame for simple inadequacies. (which we all have)
+1