When you are there, check, also between 24 and 48 hours before, people cancel as they do not want to pay the cc charge for cx. The cx deadline is 24 hours before, we have snagged a hard to get ADR the morning of.
Do not be discouraged, and again, they may allow you to walk up as well.
Good luck!
You are going to be there during a very busy time of the year. Keep trying daily and use the Touring Plans reservation finder. In no way would I count on doing a walk up at BOG during the holiday season.