There are other platforms that enable you to offer hourly work and track the hours through the platform but Fiverr just doesn’t work that way. You could try the milestone payments instead.
I’ve worked on other platforms and, in my experience, clients are very unrealistic when it comes to what is doable in an hour. It’s either naivety and/or an attempt to keep the fee as low as possible. One example I can give you is being asked to record, edit, and deliver an audio book of 10,000 words in the same day. “It’s about 90 minutes work so I can offer $20.” The timeframe and price are both laughable and I always turn these offers down.
You’d be saving yourself many headaches by removing the one hour option. If it’s possible, offer a word count or a page count. Anything that will help you manage client expectations.