There is a bottle recycling bin, with one lonely bottle inside. Every hour, on the hour, people come and put bottles into the skip. The first hour, at noon, one person came and put a bottle in. One hour later, two people placed a bottle each into the skip. An hour later four people placed a bottle each into the skip. This doubling of people continued until 11pm, when the bin was finally full. When was the bin exactly half full?