How can I get this form to accept one submission per email address per day, but can vote again the next day?

We have a Unique Question feature that you can use to achieve this. 

Considering that you want to limit your user to one submission per email address per day, you will have to use 3 fields to achieve this (email field, date field and text box field). You have to pass the values from email and date fields to Text box field with conditional logic as strings (A-Z) and set the unique question limit based on this field. 

Conditional Logic Inserts Text/Calculation Into A Field

How to set Form Limits Based on a Unique Question

You can set a date field to show current date and hide it. You can also hide a Text box field that is used to get the values from the email and date field. 

Here is my demo form: https://form.jotform.com/72773832779978 

Feel free to test it and clone it. 

Hope this meet what you are looking for.

Thanks so much, but I'm having trouble getting it to work on my very long
already existing form that is a ballot for a BEST OF contest. How can I use
your form and add it to my existing form?
*Leah Bruner*
*Owner/Editor*
The Twin-City News & Tri-County Tribune
114 E. Columbia Avenue
P.O. Box 2529
Batesburg-Leesville, SC 29070
803-532-6203
BLTwinCityNews@gmail.com
www.twin-citynews.com
...

I inspected your form an I saw that you added Date and Email&Date fields to your form. However, you did not set the condition to pass a value from the Email and Date fields to Email&Date field. You have to set your condition like this.

You also have to disable Unique Submission feature, because it will prevent your users to submit the form the next day. Set it to No Check.

Here is my cloned form: https://form.jotform.com/72775086879982 

Feel free to test and clone it. 

Hope this will help. 

Can you help me do this form for the email choice where they can't submit
without providing their email address?
Thanks so much!!
*Leah Bruner*
*Owner/Editor*
The Twin-City News & Tri-County Tribune
114 E. Columbia Avenue
P.O. Box 2529
Batesburg-Leesville, SC 29070
803-532-6203 <(803)%20532-6203>
BLTwinCityNews@gmail.com
www.twin-citynews.com
...

Do you want to prevent your users to submit the form without entering an email address? 

If so you need to make your email field required. You can do it inside of the email field properties.

 

But will it mess up the existing form condition we created?
Leah Bruner
Owner/Editor
The Twin-City News & Tri-County Tribune
114 E. Columbia Ave.
P. O. Box 2529
Batesburg S.C. 29006
803-532-6203
Sent from my iPhone
...

On behalf of my colleague, no it will not mess up the existing conditions. It will just prevent the users from submitting the form if the "Email" field is empty or contains invalid format.