Bookmakers only close their gates on live bets. I frequently bet on sports events, especially soccer and I have never seen bookmaker closing their gates on any event except live bets.
Btw has any casino done any kind of poll about who is going to win? I'm seeing polls of BBC and other media, they all favour Kamala Harris. This betting moment is a huge moment for every casino, they are lowering odds for Trump but increasing for Kamala. It will be cool if any casino hire own, independent team and makes a poll in US states. It will cost a lot but I think that marketing strategy can be built around it and the casino can financially profit.
As far as I know, bookmakers calculate odds factoring in two components:
1. What people bet. If someone places a big bet on one side it lowers the return you get for that bet and raises the return on the other side.
2. Statistics they handle.
I don't put my hand in the fire that everyone does it this way but at least that's the way I understand it is.
By the way, does anyone know until when it will be possible to continue betting for the US election in MW? I imagine until the polling stations close, no?