ValidTime:

-------------------------------------------------------------------------------
   Returns the time if valid. Otherwise returns empty. Valid time is
   in the for 00:00:00
-------------------------------------------------------------------------------
   Form:
   d = ValidTime( t )
-------------------------------------------------------------------------------

   ------
   Inputs
   ------
   t             (1,:)   Date string

   -------
   Outputs
   -------
   d             {:}     Fraction of day

-------------------------------------------------------------------------------

Children: