Hi Stephanie,
You'd need to have a flow step or campaign set up to populate that data at the time the form is filled out. Basically, you'd have a custom field and a trigger campaign that would use the trigger Fills Out Form > Is Any. The flow of that campaign would use a Change Data Value with the {{system.Date Time}} token to populate your custom field with the current date and time. Then you could include that custom field in your spreadsheets to show when the most recent form was filled out for each lead.
The only issue is that this will only work for leads filling out forms in the future. There isn't currently a way to export the day and time of a form fill-out en masse automatically.
John