When you create a campaign, you can apply a delay. In the case of a signup form, recipients will begin receiving emails after they sign up to your mailing list.
The delay of any messages is based on the recipient's initial sign up date/time or when the delay has been applied. If you have a message that sends after a 1-hour interval, and another after 1 day, the cycle of emails would begin as soon as the recipient signs up. This results in the recipient receiving 1 message an hour later, and a second 1 day later.