I am new to this but I will tell you what I've been told.
Adding timing is to increase power of motor.
Start RPM and end RPM is the range that the "turbo" runs in.
I run the 1/10 AE B4.1 with start RPM at around 5000 and end around 20000.
What this does is it kicks in the turbo when the RPMs goes over 5000 rpms. Because the range is large, the burst is smooth. For example if start was 5000 and end was 10000 the turbo would be stronger faster. I also run a little higher start rpm so the turbo does not kick in on the turns of "s" and throw the buggy out of control.I hope this helps. Just test it by making small changes and turning a few laps.