Gralab 300 is not accurate enough for repeatability, especially for short times. You should go with a digital timer.
I use a Kearsarge 301, and highly recommend it: built like tank, very simple logical design, has everything i need, and more importantly nothing i don't need. This thing must be designed by someone who actually prints.
I use a Gralab 300 for film development, moving hands are perfect for inversions. And i actually have a third timer, Gralab 451, in the tray area. This allows 2 different sequential time programming, so everytime i press "start", it alternates between developer and fixer time.
This whole arrangement may seem like overkill, but when one spends a lot of time in the dark, anything that saves time and frustration pays off. Everything stays in its place and ready to use.