Cast to Datetime from generic type value.

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
  class Program
  {
    private static void Write<T>(T value)
    {
      if (value is DateTime)
      {
        var datetime = (DateTime)((object)value);
        Console.WriteLine(datetime.ToString("yyyyMMddHHmmss"));
      }
      else
      {
        Console.WriteLine(value);
      }
    }

    static void Main(string[] args)
    {
      Write(DateTime.Now);
      Write(1);
    }
  }
}