Example
//default DateTime patterns
worksheet.Cells["A1:A25"].Style.Numberformat.Format = DateTimeFormatInfo.CurrentInfo.ShortDatePattern;
//custom DateTime patters
worksheet.Cells["A1:A25"].Style.Numberformat.Format = "dd-MM-yyyy HH:mm";
//or overwrite the patterns in the CurrentThread with your own
Thread.CurrentThread.CurrentCulture = new CultureInfo("nl-NL")
{
DateTimeFormat = { YearMonthPattern = "MMM yy" }
};
worksheet.Cells["A1:A25"].Style.Numberformat.Format = DateTimeFormatInfo.CurrentInfo.YearMonthPattern;
