I did this in zshrc:
## 2018-08-10: ticking clock:
#RPS1=$'%t %w'
RPS1='%B%F{yellow}[%D{%L:%M:%S}]%f %w'
TMOUT=1
TRAPALRM() { zle reset-prompt }
Nice to have the time ticking away there, but it kills back-scrolling --
I scroll up, but every tick moves back to the bottom. Fixable?