MATE (Gnome 2) and Cinnamon (Gnome 3) are two different Desktop Environments, so the chances of installing the Cinnamon digital clock in MATE are very slim.
MATE however does have screenlets.
To install screenlets you first need to install this PPA:
Then install digitalclock-screenlet:
sudo apt-get install digitalclock-screenlet
I should warn you that the clock is bright green and pretty hideous, in my opinion.
If you subsequently wish to remove it:
sudo apt-get remove digitalclock-screenlet