GlideDateTime
The GlideDateTime class is for working with date/time fields and date/times in general.
Constructing a new GlideDateTime object using the new keyword with no arguments initializes it to the current date and time in GMT. You can also initialize while passing in an argument: either another GlideDateTime object or a date-formatting string (in the UTC timezone) in the format: yyyy-MM-dd HH:mm:ss.
Adding or removing time
There are multiple methods for adding or removing time from a GlideDateTime object once it's initialized. Here are a few of the more useful ones.
The add() method accepts one of two types of arguments: either a GlideTime object (an object containing a specific duration or amount of time) or a number of milliseconds.
You can add a specific number of days (local time or UTC) using addDaysLocalTime() or addDaysUTC(). Neither method returns a value.
The same is true for adding time week-by-week (addWeeksLocalTime()and addWeeksUTC()), month-by-month (addMonthsLocalTime()and...
