I'm in the metronome camp too - there is a timer in-line but I only use its on/off switch. A piece of black foamboard waved under the lens begins and ends the exposure (or if I'm burning sky, I use that card).

In contrast, I use my laptop to time processing of both film and paper (Jobo for film & a red safelight filter over the LCD screen for paper. Free software called LeLab available here does the film & paper timing.