How to select custom waiting time before putting screen to sleep in Mate Power Management?
You can set these options using commandline
gsettings set org.mate.power-manager sleep-computer-ac 1800
gsettings set org.mate.power-manager sleep-display-ac 1200
gsettings set org.mate.power-manager sleep-computer-battery 180
gsettings set org.mate.power-manager sleep-display-battery 120
where numbers are seconds.