How often can one person hear from me?

Nobody gets more than one message from you in a day. While you hold pack credits the limit is two: the pack is what buys the second. When the pack runs out, it goes back to one on its own.

The line under Target Audience on Notify says which limit applies to you right now.

Every message to that person counts, whether you typed it or it sent itself. When you count a group, anyone who has already had their message today is left out, so you are never charged for a message that would not arrive. A message that sends itself to someone who has already had theirs that day is skipped for that person.

Messages on your wallet pass follow the same rule, counted on the pass. Apple and Google also have their own daily limit for one pass. See How often can I put a message on somebody's pass?.