Our use of the clock and the calendar are so ingrained that sometimes it's hard to imagine that things can have ever been otherwise. But they can, and in The history of time
Leofranc Holford-Strevens has given us lots of information about how the ways we describe time have come about. For instance the word noon comes from the latin for 9 meaning 3 o'clock in the afternoon - work that one out if you can! The book is mostly concerned with the history of the current calendar, but also has information on time-keeping in other cultures such as the Mayan calendar.
This book is part of the Very Short Introductions series, but I felt in a way that it doesn't really fit. Holford-Strevens has done well to fit such a lot of information into a short book, but it does mean that its not so easy on the reader - I felt that there was more than I would ever want to know about how the date of Easter has been calculated. It's not so much an introduction, it's more like a pocket reference. But if that is what you want, and you don't fancy the author's longer Oxford Companion to the Year then you should consider this book.