40 minutes wait for an appointment where you are on time for is NOT running late. THAT is a fault of in house scheduling and not imposing penalties for anyone that would cause them to "run that late". You don't punish on time, reliable customers for the misdeeds of other mongers. If someone is late for their appointment....you let them run out the clock on their dime. Ten minutes late....50 minute session. Twenty minutes late.....40 minute session. You don't cut into someone elses time or make them wait for the faults of others. Just poor business sense.
My best chances for on time appointments is usually when it’s not busy (obviously) but it’s difficult to time that as well.