The first book is great for K-2nd. A Second Is a Hiccup introduces students to the basic units for measuring time by comparing them to real-life examples and familiar situations. The book introduces seconds, minutes, hours, days, weeks, months and years.
My second recommendation is Me Counting Time: From Seconds to Centuries. This book also introduces (or reviews, depending on your grade level) students to the units of measurement for time, however, it includes larger units such as decades, centuries, and millennia, making it appropriate for older grades as well. It presents an opportunity to discuss how we covert units of time, for example, 10 years is equal to 1 decade. I'm thinking that I will present some of my stronger math students with some time-related story problems.
What are you learning about in math? Be sure to check out other math mentor texts over at Collaboration Cuties!
Have a great Sunday!