Understand that once a social security number is marked as "claimed" for the tax year, amending a tax return will not change that. If your son is amending his tax return to change his status to "I can be claimed on someone elses return", you will still have to mail your amended tax return to the IRS.
Amended tax returns normally take 8-12 weeks to process. But now-a-days it can take months due to the IRS backlog. I know a few who waited more than a year from the time they mailed their amended return, before it was processed by the IRS.
