If you are looking to make a campaign longer, the proper way of doing this is by adding an Email, Text Message, or Voicemail to your campaign.
Please note: When adding Email, Text Message or Voicemail it doesn't mean you add 1 day for every message added. You still have to select when exactly this message goes out.
Ex: You could have 10 messages that go out in 1 day, or 3 messages that span 10 days of time. You get to choose depending on the needs your campaign is trying to meet.