You have many options when it comes to scheduling your campaign:
Send today - You can send the campaign either immediately, or at a specified time today
Send a certain number of days/weeks/months/years before or after a custom, or subscription date. You can set to run this campaign once or every year. An example of its use is:
Send a birthday message 3 days before the contact's birthday
Send a reminder 1 week before the anniversary of their purchase with you