As in the object. Could not find the information with a site search.
Yes. Proposals are automatically closed if they do not complete the commitment phase in 4 months or less.
This is done to ensure the proposal has enough committed users to succeed as an actual site. Before this rule was made, there were quite a few proposals that took a long time to make it out of commitment, and ended up being closed soon after starting private beta.
See also: Changes to the Area 51 Process v3.0.