I think it starts with the 6th inning, but not 100% certain. Books used to have 1st half with some at 4.5 and others at 5 innings, but I think they all went to 5 innings.
Cris is odd with the second half only good before game starts, I'd like to see it available up to the 6th inning starts.
You can't bet the 2nd half of anything I know of until the 1st half is played, but you can bet the quarters, pretty strange.