I had the same issue, and I knew I must end all those ‘urgent’ calls on the weekends from my clients. I usually send something like this:
I just want to follow up and check if you have any questions related to your site and back-end. I am always here to help you with my advice. I also want to mention that a big part of my expertise is providing professional website maintenance and technical advice, so I am always here to answer any of your questions after the site is live. I provide free support for 2 weeks after the site is created, and after this period I bill for email, phone and face to face consultations with 15 minute increments and a rate of $40/hour. In case you need more consistent support every month, I also offer a monthly fixed price plan.
Same here. By making it clear about support fees and my office hours, I ended all the annoying calls on Saturday evening from a client asking about random things. I am still available anytime for emergency situations (such as hosting failure), but as it turns out, usually they can wait until Monday :).