Most therapists work 9-5: most of their clients don't. Therapists may not be aware of conflict between their schedules and their clients'.
We base our assumptions about normality on our own experience and risk mistaking the norms of our immediate social circle (or movies and TV) for demographic reality.
I was asked to help stroke ward staff manage a patient who took his bed very early in the evening and woke correspondingly early in the morning. Most hospital patients have difficulty being woken at 6am: this gentleman was up at 4am. The concern was that the stroke had damaged his body clock. In fact, he was a farmer, following his normal sleep routine of sixty-eight years!
Most people work 9-5, apart from farmers, students, factory workers, children, supermarket staff, retirees, taxi drivers, cleaners, restauranteurs, post office workers…
Working 9-5, Monday to Friday is a pretty middle-class, professional schedule … and maybe not even that: hospital nurses, medics and other staff (e.g. radiographers) work shifts and anyone employed by an international company may be required to keep the hours of their colleagues in another time zone.
An "abnormal" daily schedule — in the eyes of their therapist — can reduce the chances of a client engaging in therapy. Continually offering a single mother an appointment at the time school ends turns therapy into one more stressor. Therapy may even have to take a break during the school holidays.
Sleep or meal times at odd hours — long distance lorry drivers may be eating their dinner at "breakfast time" — can make a diet sheet or sleep diary difficult to interpret and may, if not fully understood, lead to impractical advice being offered.
Sleep and work routines may form as much of a culture as race, nationality or ethnicity. There are people who have worked night shifts for decades: counselling disruption of their longstanding routines could be as "culturally insensitive" as challenging any taboo about food, dress or physical contact.
Making the daily routine an initial interview question can help maintain awareness that your "normal" day may not be your client's (or your colleagues'). You may not know your client's schedule when you offer the first appointment, but there's little excuse for not knowing when to offer the second.