DateTime Epoch = new DateTime(1970, 1, 1, 0, 0, 0, 0, new System.Globalization.GregorianCalendar(), System.DateTimeKind.Utc); sb.Append("\"\\/Date(" + ((dt.Ticks - Epoch.Ticks) code example

Example: c# convert Unix time in seconds to datetime

public static DateTime UnixTimeStampToDateTime( double unixTimeStamp )
{
    // Unix timestamp is seconds past epoch
    System.DateTime dtDateTime = new DateTime(1970,1,1,0,0,0,0,System.DateTimeKind.Utc);
    dtDateTime = dtDateTime.AddSeconds( unixTimeStamp ).ToLocalTime();
    return dtDateTime;
}