My son accidentally checked that he was not to be claimed as a dependent. he has since amended his return. how soon after that can i then submit my return without it being rejected and his staus

Not this year at all.   Once a SSN is used the IRS will not allow another e-file with the same SSN any time this year.   You can only print and mail file.   Amended returns also take 16 weeks (4 months) to process.