Why would Alito allow Pennsylvania until Dec 9 to respond?

If SCOTUS declared the Pennsylvania election voided — and did so after the 8th but before the 14th, it would prevent Pennsylvania from naming electors to the Electoral College.
~ @shipwreckedcrew https://redstate.com/shipwreckedcrew/2020/12/05/is-there-another-scenario-that-makes-justice-alitos-dec-8-response-date-meaningful-in-different-way-n289672

That would shut the state out of the process of electing the next President. This would be justified by the fact that the Pennsylvania General Assembly and the elected officials of the State Government are all to blame for the manner in which the election was conducted.

"They violated the rights of all Pennsylvania electors who were entitled to vote on the Constitutional Amendment adopting 'no excuse' mail-in voting by imposing that scheme through Act 77 in violation of the Constitution."

If SCOTUS invalidates PA's election because its expansion of vote-by-mail was unconstitutional, it may invalidate Wisconsin's, which expanded vote-by-mail without the legislature's consent. GA's change of signature verification was likewise done without the legislature's consent.

If the elections of those three states (or any two states plus Pennsylvania) are invalidated, Biden does not get 270 electoral votes.
It then goes to the House.
1 state, 1 vote.
Rs have the majority.
POTUS is re-elected.