I haven't placed a vote. I think this kind of thing is too subjective to put a simple time scale on. It needs judging case by case.
Perhaps it could be an option for the severity of punishment based on the crime. Like, banned, but allowed to appeal again in x amount of time, or banned with no future appeals.
Personally i don't think they should be able to, BUT after a year if they want a second chance and are willing to prove themselves i say let them have an appeal.
Anything less is way to short a period of time in my opinion.
Only thing is i think that any bans without appeals shouldnt get another chance
People have a decade+ to figure out all this stuff from real-world concepts; i'm not too keen on thinking they'll entirely change within short period of time. I picked the last option.