Ed,
Not exactly sure what you mean. If you mean, insert it onto 12
different tabs/worksheets within a workbook and they're all in the same
cell (e.g. A1), you can select cell A1 in Sheet 1, and then shift click
on the final tab/worksheet. This will select cell A1 in all tabs. Press
Ctrl ; to insert the date and press Ctrl Enter to enter it onto all 12
cells spread across the sheets.
Clive