Regarding the use of the metronome, Michael Smith and Paul Chamlee of Azo/Amidol fame usually use nothing other than the metronome. To see Michael print is fun....the "printing light" is never off...cardboard over the paper until the exposure is made, then the cardboard is off while the metronome beats.... Michael "dances" about listening to the beats until the exposure is over, cardboard flips back over the printing frame. Burns and dodges are also done with the metronome....the cardboard comes off, the burn is done for a few beats ( seconds of course ) the cardboard goes over the printing frame again while the "printing light" stays on. Not having to turn off the light source makes the workflow faster. Obviously such an approach would be difficult with conventional silver enlarging printing....but now that I think of it though, I wonder.
By the way, I use the DA timer....great. I am sure the RH timer is great as well.