using System;
public static class Methods
{
    public static DateTime ToDateTime(this DateTime _DateTime, string data, string hora)
    {
        try
        {
            return DateTime.Parse(string.Format("{0}/{1}/{2} {3}:{4}",
            data.Substring(0, 2),
            data.Substring(2, 2),
            data.Substring(4, 4),
            hora.Substring(0, 2),
            hora.Substring(2, 2)));
        }
        catch (FormatException ex)
        {
            throw ex;
        }   
    }
}
public class Test
{
	public static void Main()
	{
		DateTime date = DateTime.Now.Date.ToDateTime("08072013", "1515");  
		System.Console.WriteLine(date.ToString("dd/MM/yyyy H:m"));
	}
}