Each project can use any number of libraries, which can be selected in the Logic Designer. You should only select those libraries that you will in fact use, since there is a cost in CPU and memory associated with each additional library.
Once you have added a library to a project, you can immediately take advantage of it and start using its facilities in your rules.
Let's assume that you have a table called Orders, with two attributes:
The easiest way to do this might be to use the excellent moment.js library:
This could also be done with Java objects, of course.