Do they count and declare the mail ins and early votes separately?
That would probably depend on which state it is. Each state is responsible for administering its own elections, they aren’t administered federally.
Thats the odd thing really – and part of the reason that the republican candidates in particular can win with a minority of votes. The presidential election isn’t one election, it’s 50 elections. Each state manages its election in its own way. I was looking at an example of a (I think Iowa) ballot paper from 2016 – voters would have turned up at the voting station to find 10 candidates for president on the ballot paper. Even when it comes to the electoral collage they again manage that differently. In some states all the ‘electors’ will vote for the candidate that won that state – so a candidate could win a state by one vote and all that state’s electoral college votes will go to the that candidate, in others the state will split their electors proportionally between the candidates so a candidate can lose convincingly and still gain a significant number votes towards the electoral college..
There is a bit of an odd anomaly with early, particularly mail-in voting which is they don’t necessarily count the votes but they know who has voted. Many voters declare their affiliation on their voter registration, so without counting the votes you know how many ‘Registered Republicans’ and ‘Registered Democrats’ have voted and that information is often made public ahead of poling day.