Should there be an extra charge for someone doing a day stay, but it's over 12 hours?

I assume you are talking about daycare. Rover defines daycare as "dropping off around 7-9am and picking up around 4-6pm. " That's about a 10-11 hour window.

As an independent contractor, you can set your own rules. My recommendation is to establish dropoff and pickup times in your profile and communicate them with customers. Tell them that if a dog is not picked up by x hour, then your boarding rate will be used.

I only do boarding and, if a dog's partial day stay is more than 10 hours, they are charged for another whole day because it usually means 2 more walks and 2 feedings.