Although the Federal law prohibits any convicted Felon from ever owning a gun it is possible for the convicted Felon to have their gun rights reinstated after being felon free for the 10 years.
A felon can't just get a gun after 10 years though they have to be felon free for those 10 years.
The clock starts after they've served their prison sentence.
So after they get out of prison they must remain felon free for those 10 years after the felon is released from prison.
And some states have different laws regarding whether the convicted felon can ever own a gun again so you'd have to check with your local law enforcement or other government about whether the felon can own a gun or how they can get there gun rights reinstated after being felon free for 10 years.