It looks like the date a response was submitted is included in an export of responses, but how can it be added to a report?
I have never seen anyway to include the DATE SUBMITTED field in a report. However, there is a workaround that you can use in future surveys.
1] Add a text box question to your survey and title it SYSTEM DATE (or whatever else you want).
2] Open the Logic tab and select the HIDE THIS QUESTION….. option.
3] Open the Layout tab and scroll down to the DEFAULT ANSWER field. Click on the MERGE CODE link and insert the SYSTEM – CURRENT DATE EST merge code.
Make sure that you place this question on a page where the respondent will be hitting the NEXT button. The respondent will never see the question, but the current date will be submitted when the NEXT button is hit. You will be able to use this date in reports