There are two ways to copy an autoresponder campaign. One message at a time, or duplicating the entire campaign.
To copy only 1 message from one autoresponder campaign to another, simply use the "send to" feature found in the list of messages within the autoresponder messages.
Next, select if you're going to copy this message into the same autoresponder campaign (essentially duplicating this message) or into a different autoresponder campaign. Either way you can set the days delay depending on when you want this message to be sent in this campaign.
If you'd prefer to duplicate the entire autoresponder campaign, you can use the copy function found on the list of autoresponders on the "Autoresponders" page.