My boss calls and texts me at all hours and on weekends. He expects an answer no matter when. What's the best stragety for dealing with this while still maintaining my own time?

I’m in a similar situation as I’ve been asked to work independently on behalf of two separate sites because of the recent pandemic. Both sites want to keep in touch with me regarding different matters; but there’s work time and there’s my time. These should never overlap; especially if you’re being paid by the hour for a large company. But it’s difficult to turn around and say no as there’s often urgent matters that need to be resolved regardless of who’s the cause of it. Refusing these messages makes you seem inflexible and could have an impact on your career progression, but you also have a life outside of the workplace. That's why I keep a log of how much time I've spent outside of the workplace dealing with these messages. Then when I'm in the workplace, I’ve got evidence to claim the time back. This could be in the form of an overtime payment discussed with the boss, or Ican use the evidence to leave earlier at the end of my shift. I also use it to justify arriving late one morning, or take slightly longer breaks for the inconvenience. If you’re not being paid for it, it’s important to claim it back.