Setting Email Based Action in Autoresponder

Hi. I currently have an autoresponder set up to deliver an email when a lead signs up to be on our email list. If the lead does not open the email with 48 hours, I want to send another version of the email. I am unsure how to set this up.

Do I create a follow up message in the sign-up autoresponder and then configure the Send Settings after the email is reviewed? (I can't see what options are available in the Send Settings before submitting the email for review and so don't know if this is possible).

Or do I create a separate email action autoresponder to send the follow up email if the first email was not opened within 48 hours? (The option in this email action autoresponder to select Open the Email appears to refer the email that I would set up in this second autoresponder and not the email associated with the first autoresponder.)

Thank you.