BOG for breakfast and lunch is filled by head count - not number of diners and number of tables. If there are 300 spots (I don't know the number - which is set by the fire marshal) - that is how many guests they allow to have reservations for. You got the last one. When another opens up, you can grab that one. The times can be anywhere in that first hour if you want PPO. Everyone is seated when they arrive at that time.
You should have not much trouble picking up another single. We recently scheduled a trip 2 months out. The three of us ate at BOG 4 mornings - all PPO. Most were single reservations.