/// <summary>
/// （在两个时间范围内）生成随机日期
/// </summary>
/// <param name="startime">开始时间</param>
/// <param name="endtime">结束时间</param>
/// <returns>返回随机日期，如（2014-12-25 00:00:00）</returns>
public static DateTime RandomTime(DateTime startime, DateTime endtime)
{
    Random rd = new Random();
    TimeSpan tsp = endtime - startime;
    int days = rd.Next(0,tsp.Days) ;
    DateTime newtime = endtime.AddDays(-days).AddHours(0).AddMinutes(0).AddSeconds(0);
    return newtime;
}