I really find value in those moments...and need them.
I have literally almost been brought to tears with intrusions from those select few in our society that can't take a hint, think they are much more interesting than they are, and have no concept of personal space and the importance of solitude.
I am also not too terribly anti-social, but I crave solitude and alone time. It just so happens that my go-to favorite spot is in the same town that I work and most people there recognize me and know me from my position, which gives them more liberty with my time than they should allow lololol and it also leads them down crazy questions and conversations when they catch me "off duty"
Needless to say, I feel your pain on this one and I am here to tell you flat out you are well justified in your feelings and you doe NEED this time.
I welcome a chat and coffee with others, and also my own time. I guess the trick for others is to know when to approach and when to wave hello and move on. I don't blame people for intruding though, I mean it's a public place. I played it up a little in this post. Had I wanted complete solitude I wouldn't have been there.
We all need, or should find, time for ourselves. These days it's so easy to get bogged down with unimportant stuff and finding the ability to shut it out is important.