How fast do they count the already received ballots? Why wouldn't they call it at poll closing time the way they do most Presidential elections. It's doubtful this is going to be close.
~71% of final 2020 votes were counted within 24 hours, the soonest timestamp I got on 2020 election archives. This lines up with the little under 70% of votes which were in the counties possession and verified before election day, so it seems like these were all released fairly quickly. The majority of the remaining votes were processed over the next few days, with the stragglers taking forever to process. Of course the stragglers matter in tight house races that get all the attention, so California earns a reputation of taking forever to count.
What's stopping a poll-closing call is the lack of an exit. It is technically a not a partisan race, so you can't simply look at prior records and declare it done. You would need a bit of data, say that 70+% which will quickly report.
See my previous post for data on the partisanship of the 2020 vote count.
Poll
