I don't see the problem. You're just asking to pay more? If they're done in two hours, they'll either charge you less or leave, so you pay $55. In your example,

I don't see the problem. You're just asking to pay more? If they're done in two hours, they'll either charge you less or leave, so you pay $55. In your example, that two hour cleaning is now $70. Additionally, I think you're underestimating the amount of time a good cleaning can take, even of a smaller apartment / studio.