The U.S. Census detailed data that states need to redistrict U.S. House and state legislative seats will not be available until September 2021. The National Conference of State Legislatures has an article about what states can do about that problem. The most interesting idea is that states should postpone their 2022 primaries.
The range of time for congressional primaries varies widely from state to state. Illinois and Texas have their congressional and state office primaries in March of election years, but a few states don’t have them until September of election years.
Ballot access for independent candidates and unqualified parties is better when major party primaries are later. A significant number of states continue to tie the independent petition deadline to the dates of primaries. So the later the primaries, the more time for independent petitions to circulate.