You can set a time for your form to start accepting submissions, a time for it to stop, or both. Before the opening time and after the cut off time, uploaders get a short message instead of the form. Scheduling is available on the Business and Premium plans.
Both settings live in Security & Limits, and both need the form published to do anything. Turning on the opening time setting shows the note "The form must be Published to be scheduled."

The two settings are independent. Set an opening time on its own for a form that should go live overnight, a cut off time on its own for an open form with a deadline, or both for a window.
If you set both, the cut off time has to be later than the opening time. EZ File Drop will not save a form where they are the other way around, or where the two times are identical. The message "The start time must be earlier than the cut-off time." appears under Starts at, whichever of the two you changed last.
The times you set use the Time Zone on your account, which you choose on the Profile page. If you have not set one, they use your browser's time zone instead. The setting names the time zone it is using directly above Starts at, so you can check it without leaving the panel.

Uploaders elsewhere see the form open and close at the matching moment in their own local time, not at the clock time you typed. Meridian Creative, in California, sets a form to open at 12:00 AM on August 2. An uploader in New York can start uploading at 3:00 AM on August 2 their time.
Worth keeping in mind when your deadline matters to people in another time zone.
A card with a clock icon, the heading "Form Not Yet Open", and your message beneath it.

A card with a circled X icon, the heading "Form Unavailable", and your message beneath it.

A published form waiting for its opening time has the Live status, the same as any other published form. It is not a Draft, and nothing about it needs fixing.
That matters when someone tells you their upload is not going through. There are two different reasons a form might not be taking submissions: it was never published, which is the Draft status, or it is published and outside its scheduled window. Check the status first, then the schedule. See Form statuses.
You get an email within a minute of the form starting to accept submissions, and another within a minute of it cutting off. Moving the opening time to a later date arms the first email again. The cut off email is sent once per form, so a form given a new cut off time after the first one passed does not send a second one. To send these to other people as well, add them in the Notifications tab. See Set up email notifications.
Switch the form canvas to Scheduled - not live yet or Cut off time reached, then click an element to open its settings. See See your form's states.