It is important to have a structured workday that is planned during times that are less likely to interfere with the instructor's concentration and progress but also important to establish boundaries and to explain those boundaries to students and stick to them.
I tend to be "available" at all hours except when I am actually sleeping, which the students appreciate, but it does create expectations that I will always respond quickly at any time of the day or night. I need to establish a set time period and stick to it.
