If you ever want to hire anyone on upwork, never do an hourly unless you are comfortable with hourly. There is protection on UpWork whereby even if you are not happy with the work being done, you still need to pay the Freelancer. Even if you have an agreement in the UpWork chat, it doesn’t matter… the freelancer gets paid for their hours. The only thing you can do is notice what is happening and cancel your payment method BEFORE Upwork invoices you so that they can’t take money out of your account.
In many cases, the freelancer working hourly isn’t being honest with their hours and will try and steal hours from you. What will happen is that UpWork will try to get you to pay. They will then suspend your account. At some point they will re-evaluate the hours of the freelancer and find the discrepancy. They will restore your account and you don’t have to pay the freelancer.
We don’t recommend this as a general practice but freelancers (particularly overseas ones) seem to want to take advantage of loopholes in UpWork.