How to implement that the pets should be picked up at a certain time?

Your operating hours and procedures should be documented in your profile as well as discussed with the client when you have your M&G. I get the dropoff and pickup times before it is booked, so that I can insure the billing accurately reflects the amount of time the pet is staying with me. I tell them that each night of boarding is only good for up to 24 hours; therefore, they need to pick up their dog at approximately the same time as they dropped it off. I do allow a bit of leeway (4 hours) but I don't tell them that, as I would expect some to push the envelope.

So try to get the info before so it can be billed initially because Rover's system doesn't allow for "late fees." Since you do offer daycare, you do have the ability to charge them that if they're late, and you can adjust that amount as you like, consistent with the overage.

But make sure the client understands they will be charged, and the bill paid, before they can pick up their dog.

I noticed that quite a few of your reviews mentioned how "flexible" or "accommodating" you were on times. While that can be a positive, it ciould signal people have taken advantage of you.