Be on time for your appointments & consultations. Punctuality conveys professionalism, respect and allows you to address & manage possible resistance on the part of the client.
There's a Catch-22 type joke (at least, I thought it was a joke) about clients' attendance at appointments:
If they're early, they're anxious; if they're on time, they're obsessional; if they're late, they're resistant.
Therapists, by contrast, seem only to have two modes: on time (rare) and late (mostly). Lateness on the part of therapists is usually due to an excessive workload and so is likely to be forgiven—or at least tolerated—by NHS clients. The implicit message, that the therapist's time is more valuable than the client's, doesn't make for a good start to a session, however.
In an over-subscribed service, punctuality is difficult to ensure. Many medical services don't even try, overbooking clinics on the principle that there will be non-attendances. The aim is to ensure that the clinician never has to wait for a patient, but this almost guarantees that the patient will face a lengthy wait.
Punctuality has no downside. Lateness may imply importance and high demand, but punctuality conveys professionalism, courtesy and credibility: who would accept time management advice from someone who arrived late?
Ten minutes in a busy clinic can be a very short time: scribbling casenotes, fielding phone calls and requests from colleagues, scanning files and letters prior to your next appointment.
Ten minutes in a waiting room is a long time, especially if you have arrived early in order to ensure that you are on time, if you are anxious or in pain, or if you have psyched yourself up for the appointment. A punctual therapist will get a calmer, less anxious client.
Therapists who book appointments back to back (or overbook clinics) to compensate for non-attendance are replacing one problem with another. Punctuality ensures that persistently late clients are obvious to the therapist, not just their receptionist, permitting contributory issues to be addressed. Tackling client lateness when you are habitually late would be a challenge for even the most blatant hypocrite!