Option "OffTime" "time"
sets the inactivity timeout for the off phase of DPMS mode.
time is in minutes, and the value can be changed at run-time
with xset(1). Default: 40 minutes. This is only suitable for
VESA DPMS compatible monitors, and may not be supported by all
video drivers. It is only enabled for screens that have the
"DPMS" option set (see the MONITOR section below).