My understanding is that Breyer is retiring at the end of the SCOTUS term, which is 3 October 2022 (1st Monday). The mid-term is 8 Nov.
However, they normally recess in early July and stay recessed until the next term starts. Hopefully that means we have ample time for hearings and confirmation well before the midterms. ACB was confirmed in 30 days, hopefully that is a precedent we can use to our advantage.
The Senate only needs a simple majority to confirm so hopefully that part will be OK. The only possible 'snag' is that the Judiciary Cmte needs a 'quorum' to vote in Committee and thus move the nomination to the Senate floor. If all of the 11 GOP Judiciary Cmte members refuse to attend, we may have a problem. I don't know what would happen then. And I don't know how many of them are hardcore Doofinistas or susceptible to pressure blackmail from Doofus.