#!/bin/shAs you can see I've named it setscreendimtimeout and put it in my ~/bin dir (and of course made it executable with chmod +x).
echo "Usage: setscreendimtimeout [seconds]"
gsettings set org.gnome.settings-daemon.plugins.power idle-dim-time $1
Test it out with setscreendimtimeout 2 and see if your system is even more annoying - then set something reasonable for your use...