Yes, you must wait 30 days from your initial sign up before you can submit an expense and that expense has to have occurred after the waiting period ends.
One frequently-used method of fraud comes from individuals who have upcoming expenses and join the system, get the expense paid for, and then drop. This is unfair to the honest members and it's an issue that really frustrates us.
We want members who are committed to protecting each other’s pets. The ideal situation is that your protection starts immediately - but we have learned the hard way, that when we do this, the frequency of fraud and abuse of the system heavily outweighs the small percentage of owners that experience a bad mishap during that time.