Same problem today, it started working from 3am to 10am, then crashed at 10am and can't get past map loading screen again, just locks up.
And just noticed a message about servers being at capacity after just starting up civ. Is there some sort of server connection going on even in singleplayer map loading that gets bugged at high pop times for some people or something?
I've checked everything on my computer, gpu and cpu are doing great, well within healthy parameters (temps/usage). But I stop being able to play at 10am and it doesn't start working again til late at night.