It is early 1970's Does not look toasted. Is it still ticking? is a fair question. Is it running or toast? These actually have some value unlike other Slimexes
If you look at the back - with the word TIMEX upright there should be a little "lip" on the bottom of the cover. Slip the blade of a "junker" penknife or a utility knife it to pry it off.
It will likely bend the edge of a good knife so use something you don't want to keep nice.