To change the form’s activity go to My forms and click the show more icon near your form. Select Activate/Deactivate.
Setup your form status here: always active, active between, active only for me, inactive or active only on certain days of the week. This gives you quick control over the time span during which the form can be accessed by users. The feature is especially useful with registrations or contests, where you want to make sure that no overdue submissions are made.