Dates & Times

DateTime and TimeSpan both use ticks to represents time.
A tick is equal to 100 nanoseconds (or one ten-millionth of a second)

DateTime_IsValidDate
DateTime_IsValidTime

default to "01/02/2001 12:00:00 AM" when you use System.DateTime

IsDate - does it/should it recognise UK and/or US formats or is it PC/System specific/dependent ??

Is today the first day of the current month

If Date.Today.Day = 1 Then 
   System.Console.WriteLine("First day of the month") 
End If

How many days have passed since January 1

Console.WriteLine(DateTime.Today.DayOfYear)

Get the currrent time - note that ticks are included

Console.WriteLine(DateTime.Now.TimeOfDay)

The TimeOfDay property returns a TimeSpan object which represents a difference between dates.