Find the unix timestamp for a given date

Question

I am trying to find the unxi timestamp for a given date. I wrote the below function but it does not seem to produce accurate results. Here are the results it returns and what PHP returns. Can anyone see a problem with the code?

08/25/2007 11:43:00 AM
C# = 1188042180
PHP = 1188060180

08/25/2007 11:43:00 PM
C# = 1188085380
PHP = 1188103380

        public long GetEpochTime(string dDate)
        {
            DateTime fDate = Convert.ToDateTime(dDate);
            TimeSpan ts = (new DateTime(fDate.Year, fDate.Month, fDate.Day, fDate.Hour, fDate.Minute, fDate.Second) - new DateTime(1970, 1, 1, 0, 0, 0));
            double unixTime = ts.TotalSeconds;
            long lUnixTime = Convert.ToInt64(unixTime);
            return lUnixTime;
        }