There are many timely links in the Sites By Subject section of the library's webpage. Look under Quick Reference: Almanacs, Quick Reference: Calendars and Holidays, and Quick Reference: Time for several online information sources.
Or take a look at A Walk Through Time: The Evolution of Time Measurement, the site maintained by the Physics Laboratory of the National Institute of Standards and Technology. The site includes some fascinating history on time measurement, as well as links for synchronizing your computer clocks via the Internet. Or you can go straight to their clickable map to find the precise official time anywhere in the United States.
The Greenwich Mean Time site of the Royal Observatory Greenwich is another very enjoyable, informative website. Look at their compilations of time FAQs (for example, why midnight and noon are neither a.m. nor p.m.), time trivia (including quotations and poems), and links to timely sites worldwide. You can even submit your favorite "time tracks," or songs featuring time to be posted on their site.
The Britannica site on clockworks presents general information on the history and science of time measurement.
The American Watchmakers-Clockmakers Institute site includes more specialized information on horology (clock- and watch-making), with more international links.