Owners with set times for walks?

I don't think Rover requires you to walk at a specific time/miles etc. It's up to you to have this conversation with your client. It's exactly the same way you do your own private business. Always tell the client what you have to offer. Tell them you would come by between x and y hrs and see if they agree. You don't work for rover, you're an independent contractor and you set your rules the way you like. You can charge anything you like. Rover won't tell you how much to charge. I used to have a client who demanded 5 miles in 30 minute dog walk! Normally I do 2 miles with each dog in 30 minute walk, but now since it's too hot outside, I limit each 30 minute dog walk to 1 mile only.