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You can couple this rule with an if statement in a workflow to ensure it only fires once and does not overwrite the name/email if the form is loaded in additional workflow steps.

Populate Today's Date in a Text Field

You can populate today's date in a field for the purposes of tracking when a form was initally submitted and more.  Its recommended you use this rule as a Custom Default value if you only want it to fire once.

var d = new Date();
value = d.toLocaleDateString();