At six seconds, a one second difference in exposure can actually make a noticeable difference. Whatever floats anyone's boat but for me, time is only a factor of what it takes to get a good print. Could be 13.2 seconds for all I care, since I work in f stops with 12th fractions anyway.
I don't think the OP was asking about technical things like how long your exposures are, I think he was asking if anyone has any weird habits in the darkroom.
I avoid 13 even though most of my exposures run around 12-15 seconds. I usually use my experience to get an exposure that will work so I don't see 13 on the timer or the exposure adds up to 13. My avoidance of 13 though is not rooted in mythology or anything traditional, it happens to be the date my father died. Ever since then, I have avoided the number like the plague.
A 1 second change in a six second exposure is either a -.26 or +.22 stop change - about 1/2 a zone change on grade 2 paper.
Originally Posted by MaximusM3
f-Stop timers that work in 1/12ths or 1/10ths of a stop would make a ~.4 second change in a 6 second exposure, about a 1/5th of a zone.