@youmailme,

yes it does make a difference. you have to fill another ds 160 form showing your new travel dates and ensure that all your documents are in sync with these new dates. however, you do not need to cancel your current interview appointment , just print out your new ds 160 confirmation form, log into your profile and update the confirmation number in the field with the new number. that render the previous one with the wrong dates invalid. take the new ds 160 confirmation with you to the embassy. Hope this helps,