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.