You may be right (and obviously it should be that long). It surely varies by state though, even for Federal elections the states write their own laws. That's why there are so many court battles now, many relate to different state laws.

ps

I see there is this Federal law I didn't know about https://www.wgbh.org/news/local-news/2021/01/07/now-what-happens-with-all-those-2020-election-ballots-theyll-be-around-longer-than-you-might-think

I still think it might be challenged by a crooked state as unconstitutional.

You may be right (and obviously it should be that long). It surely varies by state though, even for Federal elections the states write their own laws. That's why there are so many court battles now, many relate to different state laws.