What is the schema of your table? Could you list us the columns that contain the time information? If you have nothing in the table to keep track of the time information, then you will not be able to do this, and will need to rely on your backups (there is point in time recovery in the enterprise edition of SQL Server, so you could restore the information as of half an hour ago into a separate database)

Another thing to do: first use a select statement to see if the rows deleted are the rows you indeed want to delete.

Regards,

Andras