Set the hours you actually want to work, not the hours you would grudgingly accept. Every hour you leave open will eventually be booked, usually by the client least able to move, and the only reliable way to keep an evening is for it never to be offered.
Book your breaks as blocks so they are as real as an appointment. A lunch that exists only as an intention gets booked over by the first person who wants a one o'clock, and then it is gone every week.
Block time off as far ahead as you know it. A closure entered before the calendar opens that far is invisible to clients; the same closure entered afterwards is a conversation with everybody already booked.
Different hours on different days is normal and worth using — a late night once a week, an early finish on a Friday, a Saturday that starts later than the rest. Clients book around whatever is offered, so shape the week deliberately rather than opening everything and hoping.
Leave the last slot of the day short. The appointment most likely to overrun is the one with nothing after it to stop it, and a day that ends on time is what makes the next one bearable.