I can't even begin to imagine how much trouble it must be to use a timer. I use a metronome and can quite happily do a sixteen sec exposure with a four second dodge to that face, a couple of seconds off that side and a couple off that corner, waving my hands around whilst counting, then it's a card in and, with the metronome still clicking, a couple of extra seconds for that side and a couple for that bright spot and I'm done. How do I even do that with a timer? Eight separate exposures? Button pressing, programming? Or do they click or beep as well, in which case are you not really doing anything different? I'm quite happy to agree that I never really try for exposures under about eight seconds, just in case the variation makes a difference, but it never does, just get in the groove and it's fine.
Oh, and I did, when I started, try using a stop watch. A disaster once I started burning and dodging, no way you can look at what you are doing and look at the watch as well.
Hywel