Accountability You probably have the keys to your clients' facilities. You certainly have access to remote sites. And undoubtedly, no one else at any of your stations knows what all that stuff is. More importantly, your hours are such that perhaps no one really knows when you come and go. Make sure your billing accurately reflects the time you spend on the job.
Detailed invoices are a help.
Some engineers will knock a half-hour off their bills here and there for time spent chatting with the receptionist. Perhaps a better solution is to avoid the chat in the first place. Remember, you're a professional, and you've got work to do. You will be a better person, and a better professional if your life includes more than broadcast engineering. Furthermore, you have a better chance of being treated by your clients like a real person if you act like a real person.