# Set SECONDS to number of seconds since midnight.
export SECONDS="$(date '+3600*%H+60*%M+%S')"
# The following variables store hours and minutes.
typeset -Z2 _h _m       # Two columns, leading zeros.
# The following expression reformats SECONDS.
_time='$((_h=(SECONDS/3600)%24)):$((_m=(SECONDS/60)%60))'
# Use _time within PS1 to get the time of day.
PS1="($_time)"'!$ '
# Note that $_time gets replaced by above expression.
# Expression gets evaluated when PS1 is displayed.