If person 2 picks a dude before their slot (say 9pm, but they posted at 830pm) but person 1 still hasn't picked from earlier in the day (say 4pm), person 1 can draft/steal/take said player up untill 859pm.
To be honest, i havent seen that happen very much in all my time here, (person 1 taking whom person 2 said they would take) but, it's legal