One of the biggest benefits of a PhD is its flexibility. There are no set working hours. If you do not want to work 40 hours a week, don’t. If you prefer to have the Wednesday and the Saturday off rather than a regular weekend, do it. If you do not want to work one day, or one week, you do not have to. But unsurprisingly, this can backfire. Due to a lack of structure, what you need the most in a PhD is good time management!