>This is my understanding too. But could it be that 600,00 is a substantial number for SSMS to "deal" with? That is, my understanding is that "under the hood" when you set a column to be an Identity, the SSMS has to create temp table, set the column in the temp table as Identity and then copy all records. So the time set for this could be more than default 30 set in the SSMS. I am still, however, puzzled, why I see that the Identity is On when I thought that initially it was not successful.

Actually, SSMS does nothing of that. It only cooks a few scripts to send to the actual server, and then waits for the result and displays the results. It's just a GUI with some intellisense in it. It's something you could write in Fox if you wanted to.