If a group or person who booked a room for a certain time period is 10 or more minutes late YOU are entitled to take a room for yourself for their\his\her entire time span. It's an official policy.
Always a lot of people at 1st, 2nd and 3rd floor. 4th floor rooms are always booked nowadays. Best time to go here is at 5pm. That's if you still want to stay at that time..