It really depends on how much has to be manually counted, and when the manual counting starts. Most states in the US used to start validating and counting mail

It really depends on how much has to be manually counted, and when the manual counting starts. Most states in the US used to start validating and counting mail-in and early-voting ballots as they came in (keeping the running total confidential), and only release the numbers once the on-day polling was well under way. But under severe pressure from the "stolen vote" crowd (primarily republicans), most states are now forbidden to start counting these until after polls close, so yeah, it will take days and days to count all the mail-in ballots. Especially if (as is common these days) a large portion of the electorate votes by mail-in or early ballots. This is not a big issue if the number of mail-in ballots cannot significantly affect the result - you could "call" the return early - but for close races, yeah, you have to wait until the end. Especially because the mail-in and early-voting ballots tend to be distributed very differently from day-of-election (walk-in) ballots (demographics, political leanings, etc.)