"3 months from now, we will decide if we want to be continued working on AirBnB"
This is huge, and I think that is common in companies that join Y Combinator.
Giving time to work on the project exclusively and have to present something at the end. It forces the team to focus on the task, avoiding these questions, at least temporarily, on whether they should continue or not. At In the end, it should be easy to decide.