First of all, there is a limit to how much translating anyone can do in an hour. Of course, to some extent it depends on the translator's skill and experience, and on the nature of the material. Sometimes the translation just flows, but there are times when it is necessary to look up terms, names of people or companies, and this slows down the process. Sometimes the writing style of the original is unclear, and the translator has to spend time understanding it and conveying the same ideas in a clearer way in the target language.
Translators usually charge per word rather than per hour. Being paid by the hour would logically motivate people to work slower, while being paid by quantity should encourage faster work. A professional translator with any integrity cannot just work as fast as possible at the expense of the quality, so it's a fine art producing the best possible translation in a reasonable time.
This means that translators' income is a function of how much work they can do in an hour, times the number of hours they work per month. Most translators have busy times and dry times. Sometimes, especially at the beginning of a freelance career, there can be days or weeks without any work coming in. After acquiring a steady customer base, there can be an opposite problem. There can be times when several regular customers phone up with urgent work all at once, and the translator has to decide which jobs to accept, and in which order to do them. This requires prioritization.
When I started my freelance career several years ago, I first worked with agencies. They paid lower rates, but the advantage was a regular flow of work, and I learned a lot from the edited versions of my translations that were sent back to me. The other benefit of working for agencies is being one of the translators from their pool, so if I had to refuse a job, they found someone else to do it and didn't hold it against me.
Since I stopped working for agencies and have only direct customers, there is the risk of losing regular customers if I have to turn down any work. For example, I haven't heard from one particular law firm since I had to tell them I couldn't do an urgent job for them while I was working on something else equally urgent. Presumably they found someone else and stuck with them.
Another problem is balancing large, long-term projects with short, urgent jobs. When I translate an academic book, this project lasts for several months. During this time, I sometimes accept other short jobs from regular customers. Ideally, I would be able to concentrate only on one job at a time, but in reality I feel some loyalty and obligation to my regular customers, and I don't want to ask them to find someone else and risk losing them. So I take on these small jobs, and this delays my work on the book project.
The time management questions raised by this balancing act seem insoluble, but if any reader has any suggestions, please let me know in the comments.