Throttle the time in your business and be brutal about saying "No."

Be ultra-clear on expectations with every single client. "This is how I work. At X'oclock, I am offline and no longer available. I check emails and messages at these times only: X,Y, and Z o'clock."

If that doesn't work for them and they want someone who says "How high?" whenever they say, "Jump!" you say, "No Thanks."

But you'll find people like expectations, They like knowing there is a consistent process, an established way of doing things.

Also, find people you can trust and delegate to them.