Ever been to an onsite interview? It'll take you the same amount of time. Or longer. While being far higher pressure. And probably involve writing code on a whiteboard instead of an IDE.
Even if it is additional, it's not consecutive. The OP merely said 4 hours seemed like a long time. My point was not that this 4 hour block would or wouldn't obviate the need for the other; just that the other means 4 hour blocks are standard.