The date and time of submission will not be displayed by default.
To display date and time:
Click the form on your page.
Click Customize Form.
Click the Graph dropdown on the top right-hand side.
Click your form name.
Select Column Properties from the menu on the left.
Drag and drop the Added Time element from the menu on the right to the center of your screen.
Click Back to form builder at the top right corner.
Then click Back to site builder.
Hover over Manage and click Contact Manager or Form Data to view the date and time of form submission.