Deadline for 8862

TL; DR, how long after receiving a letter asking to submit an 8862 form do you have to send it to them?

 

I filed by brother-in-law's 2022 taxes. We ended up filing on paper because he couldn't find his previous AGI. After over half a year, he got a letter saying he needed to do the 8862 for the EIC. I kept asking him for the letter they send him with instructions. It's now been 3 months later, and he finally decides to start asking about what he needs to do and whatnot and if it's too late. The letter doesn't specify, but I don't want to give him an7 false information.

 

So, generally, how much time does the IRS give to send them back that information?

 

Thank you.