Finally got to floor 30. And considering there's only one other person in my friend list who's in fl30 too, this event is not easy nor quick, you ebolas.
No way anyone can actually complete the event in just 4 hours.
Missions in floor 21-30 can be so cruelly hard when paired with the opponent's decks you are facing. A few can take 3-4 tries to complete, and without enough LP potions (which you will run out of eventually), you'll have to wait out the LP recovery.
So no way you can finish the entire thing in just 4 hours.