If you would like a particular record to only be submitted once in a given day, you can use the following Reference ID 1:
1) Go in to the form and select the Edit button.
2) Enter PAGETYPE_DAILYSUBMISSION in the Reference ID 1 field.
This will ensure that only one record can be submitted for that specific date.
EXAMPLE: If a user submits a record on 9/26/11 11:59 PM then they would be able submit the next record on 9/27/11 12:01 AM.