Make hay while the sun shines

Make hay while the sun shines - if you have an opportunity to do something, do it before the opportunity expires.

Example - " - While my husband's out, I'm gonna watch all the movies he wouldn't let me see.
                     - Why?
                     - Make hay while the sun shines!"

Image - http://evolvingpf.com/wp-content/uploads/2014/12/make-hay-while-the-sun-shines.png