I may be misunderstanding the argument, but I wouldn’t call the time served a period during which the right was suspended/revoked simply because you can’t possess firearms in prison. It’s only a result of the rules of the facility - you also lose the ability to possess a vehicle, cell phone, knives, etc. while physically behind bars. That’s not a legal revocation of the right to possess them once you’re in a different location. To put it another way, if that’s how it worked, people who serve time for low level misdemeanors that don’t qualify for revocation in any jurisdiction (or even spend a night in the drunk tank in county jail) would need their rights restored.