I don't get the need to say you can't call at certain times unless you are calling her home number - you can leave a message and she can respond during office hours. Clients leave me messages all weekend - I respond on Monday - I use google voice and that number does not ring on the weekends or after 5 - but I don't tell people they cannot call - just that I will not respond until office hours. The same thing with email - write as much as you want and the therapist can say when or if they will respond.
If the clarification works for you then good, but I would find the therapist was making things unnecessarily complicated.