I originally read this book in the mid- to late '70s.
The premise was a bureaucracy whose job it was to manipulate events in human history by making the smallest possible change that would effect the desired outcome. Not time cops in the sense of going after law breakers. The intent was to maintain a policy of non-interference as much as possible but when interference was warranted then to make the least possible change and to do so invisibly.
For example, they might take someone's keys off the dresser and put them just out of sight underneath the dresser where they plausibly might have fallen. The subject would never know of the manipulation but would then be delayed getting out of the house and the ripples grew from there to avert a war or otherwise affect events on a large scale.
After reading that, whenever I would lose something - especially in an improbable way such as dropping a screw at my feet and then finding it on the other side of the room half an hour later - I would take some consolation in the thought that I had just averted some global catastrophe. I was pretty scatterbrained as a kid (we call that ADHD nowadays) so I experienced this a lot. Given that I've spent so much time pondering the ideas from the book, I'd love to re-read it.