Timer.js is a periodic timer that’s useful for firing up functions after a certain interval.

Timer.js is rather easy to fire up and can serve for anything from maintenance tasks to application control.

Coming with an ultra-simple API, Timer.js manages to do rather complex tasks which you will surely encounter sometime when developing an APP.

Twitter-like relative timestamps can help users not get confused in a larger interface.

Smart Time Ago, a relative timestamp plugin written upon jQuery, makes creating such timestamps easy and without any fuss.

With a simple markup, Smart Time Ago timestamps can be generated with PHP or Python from a database–using the plugin is very intuitive indeed.

Kalendae is a dependency-free calendar library that interacts with jQuery as well.

Kalendae is a rather thorough plugin and uses moment.js for date manipulations.

The calendars created with Kalendae can be attached to any element, even an unnamed one, and is fully stylable with CSS.

Kalendae’s instances can have blacked-out dates, preselected dates, and so on; plus, the library provides a thought-out callback system that’s very useful for complex operations regarding data.

XDate is a thin wrapper around the JavaScript’s Date function.

XDate, even as seen from a brief glimpse, seems to add a lot of functionality to the native date function:

• An API for subtracting and adding amounts of time to a given date;
• Chaining support;
• Useful GET functions for reducing code clutter;
• Several utilities for manipulating your XDate objects.

The library is also quite lightweight, at 7kb (2.9kb gzipped).

MobiPick is a jQuery mobile date picker inspired by that of Android’s devices.

Mobipick is a minuscule plugin, but has quite a few useful options: min/max datetime; default date; localized dates; etc.

The plugin is registered under the MIT license, and uses XDate for date manipulations, and Modernizr for input fields.

jquery.timepicker is a miniature time picking plugin written with jQuery.

There are countless jQuery calendar plugins, but this one is the first I’ve seen for actual time, not datetime picking.

Timepicker could prove useful for both to-do-list-like web apps and for everything else where somewhat exact timing is important.