I am going to submit an ITIN application for my wife this year. Since it takes at least 6 weeks to process the application and assign a number, what is the cut-off date for the application? Is it still Apr. 15 or six or more weeks before Apr. 15?

There is no cut date for ITIN application.

I know that, but W7 form should be submitted with 1040, and 1040 has a date.

The due date for tax return with or without ITIN application is April 15, 2009.

If you don't have the ITIN by April 15, you could file for an extension twhich would give you 6 more months before you have to file. However, if you owe the IRS any money you must pay that by April 15.

See: Extension of Time to File Your Tax Return

Listen, you either file both w7 and 1040 together with the balance if you owe before apr 15 OR file an extension together with the balance if you owe before April 15 .

You can file Form 4868 with BOTH of your names, your SSN and the words "ITIN APPLIED FOR" where her SSN would go. Mail that form, along with a check if you think you will owe taxes, to the tax center in Austin, Texas 73301, and you will be fine.

The cut off date is still April 15th. It may just take 6 weeks to process for a refund.