There are 3 main classes declared in <wx/datetime.h>: except wxDateTime itself which represents an absolute moment in time, there are also two classes - wxTimeSpan and wxDateSpan - which represent the intervals of time.
There are also helper classes which are used together with wxDateTime: wxDateTimeHolidayAuthority which is used to determine whether a given date is a holiday or not and wxDateTimeWorkDays which is a derivation of this class for which (only) Saturdays and Sundays are the holidays. See more about these classes in the discussion of the holidays.
Finally, in other parts of this manual you may find mentions of wxDate and wxTime classes. These classes are obsolete and superseded by wxDateTime.