My state had its results for the Presidential race declared DURING VP Harris's speech (that's AP; most of the other outlets still have it in play) so I say she was exactly on time. Results of our Senate race and House races are still undeclared. Other states are still outstanding.
What matters in the USA is that the losing candidate for the Presidency calls the winning one and concedes when it becomes clear that critical mass has been reached (this is always an estimate, because electoral votes are not yet officially committed) IN THE PRESIDENTIAL ELECTION; that already happened. You can quibble about the timing if you want, but there isn't really a precedent on that. As for her disappointing her supporters by not speaking last night, even just to say she wouldn't speak until today - I'm not going to say that no one was disappointed because everyone's an individual, but what she did - having someone else say she would speak later - is totally normal and uncontroversial in this context.
You also have to understand that in the USA, unlike the UK, the political parties who are NOT the party of government don't have a leader. Right now, Biden leads the Dems and Trump leads the Republicans; Harris has no official standing and so what she said in this speech was incredibly important. It is her one chance to speak and wrap this up. Given the things I have seen today I think her supporters were in the main happy to give her the time to get it right.
I've been in the UK for several general elections, and the systems just don't compare. If people need a UK touchpoint, I'd say a Presidential race is NOT like a General Election, where each seat has its results officially announced with every candidate standing by and speaking where appropriate, and the number of seats won adds up mathematically to who becomes PM (or, rarely, who has first shot at forming a coalition). If a comparison is needed, I'd say the US Presidential vote is more like a referendum in the UK, or parts of it. I was there too for both the Brexit and Scottish Independence referendums, and frankly I thought both were conceded too soon, without enough scrutiny, and perhaps with not as much thought put into the speeches as I would have expected. That's not a criticism of the UK (or Scotland), just a reminder that things are done differently in different places.
I think that Harris's speech comforted those it was meant to comfort, and inspired those it was meant to inspire. If that's not you and you're still sore about it, then maybe take it as a reminder that not absolutely everything ever is about you and only you.