Built-in Constants

System.DayOfWeek

System.DayOfWeek.Sunday (0) 
System.DayOfWeek.Monday (1) 
System.DayOfWeek.Tuesday (2) 
System.DayOfWeek.Wednesday (3) 
System.DayOfWeek.Thursday (4) 
System.DayOfWeek.Friday (5) 
System.DayOfWeek.Saturday (6) 

System.Globalization.DateTimeStyles

Microsoft.VisualBasic.DateFormat

This is an enumeration and corresponds to VBA.vbDateTimeFormat

Microsoft.VisualBasic.DateFormat.GeneralDate (0) 
Microsoft.VisualBasic.DateFormat.LongDate (1) 
Microsoft.VisualBasic.DateFormat.LongTime (2) 
Microsoft.VisualBasic.DateFormat.ShortDate (3) 
Microsoft.VisualBasic.DateFormat.ShortTime (4) 

Microsoft.VisualBasic.DateInterval

There is no VBA equivalent.

Microsoft.VisualBasic.DateInterval.Day (4) 
Microsoft.VisualBasic.DateInterval.DayOfYear (3) 
Microsoft.VisualBasic.DateInterval.Hour (7) 
Microsoft.VisualBasic.DateInterval.Minute (8) 
Microsoft.VisualBasic.DateInterval.Month (2) 
Microsoft.VisualBasic.DateInterval.Quarter (1) 
Microsoft.VisualBasic.DateInterval.Second (9) 
Microsoft.VisualBasic.DateInterval.Weekday (6) 
Microsoft.VisualBasic.DateInterval.WeekOfYear (5) 
Microsoft.VisualBasic.DateInterval.Year (0) 

Microsoft.VisualBasic.FirstDayOfWeek

This is an enumeration and corresponds to VBA.vbDayOfWeek

Microsoft.VisualBasic.FirstDayOfWeek.System (0) 
Microsoft.VisualBasic.FirstDayOfWeek.Sunday (1) 
Microsoft.VisualBasic.FirstDayOfWeek.Monday (2) 
Microsoft.VisualBasic.FirstDayOfWeek.Tuesday (3) 
Microsoft.VisualBasic.FirstDayOfWeek.Wednesday (4) 
Microsoft.VisualBasic.FirstDayOfWeek.Thursday (5) 
Microsoft.VisualBasic.FirstDayOfWeek.Friday (6) 
Microsoft.VisualBasic.FirstDayOfWeek.Saturday (7) 

Microsoft.VisualBasic.FirstWeekOfYear

This is an enumeration and corresponds to VBA.vbFirstWeekOfYear

System (0) 
Jan1 (1) 
FirstFourDays (2) 
FirstFullWeek (3) 

Months

public enum enMonths 
{ 
    NotSet = 0, 
    January = 1, 
    February = 2, 
    March = 3, 
    April = 4, 
    May = 5, 
    June = 6, 
    July = 7, 
    August = 8, 
    September = 9, 
    October = 10, 
    November = 11, 
    December = 12 
}