Sheet := Document.getSheets.getByIndex(0);
Cell := Sheet.getCellByPosition(i, j);
Cell.String := '00:15:00';

Cell := Sheet.getCellByPosition(m, i);
Cell.SetFormula('=M3+M4+M5+M6+M7+M8+M9+M10+M11'); //работает
Cell := Sheet.getCellByPosition(n, i);
Cell.Formula:= '=СУММ(N3:N11)'; //в Calc отображается в нижнем регистре =сумм(N3:N11)

Dim Doc As Object
Dim Sheet As Object
Dim Cell As Object
Dim NumberFormats As Object
Dim NumberFormatString As String
Dim NumberFormatId As Long
Dim LocalSettings As New com.sun.star.lang.Locale
Doc = StarDesktop.CurrentComponent
Sheet = Doc.Sheets(0)
Cell = Sheet.getCellByPosition(1, 1)
Cell.Value = 23400.3523565
LocalSettings.Language = "en"
LocalSettings.Country = "us"
NumberFormats = Doc.NumberFormats
NumberFormatString = "#,##0.000"
NumberFormatId = NumberFormats.queryKey(NumberFormatString, LocalSettings, True)
If NumberFormatId = -1 Then
 NumberFormatId = NumberFormats.addNew(NumberFormatString, LocalSettings)
End If
MsgBox NumberFormatId
Cell.NumberFormat = NumberFormatId

Cell.NumberFormatString := 'HH:MM:SS';

Cell.NumberFormat:= 41;// Тип ячейки - Время

Sheet.Rows.Count возвращает 1048576

    cursor := Sheet.createCursor;
    cursor.gotoEndOfUsedArea(True);
    address := cursor.RangeAddress;
    endcol := address.EndColumn;
    endrow := address.EndRow;