Development time

Let's say you want to contribute to PostgreSQL development and want to play by the rules (which are actually not rules, but guidelines or encouragements), such as:

1. While a release is in beta, you work on finalizing the release, not on future projects.
2. During a commitfest, you work on testing and integrating the proposals submitted for the commitfest, not on new features.
3. Major features should not be submitted for the first time at the last commitfest.

The final release of PostgreSQL 9.0.0 was on 2010-09-20. By that time you already missed the first commitfest (2010-07), and the second commitfest (2010-09) was already under way. The second commitfest was actually slightly delayed and ended on 2010-10-26, whereas the third and next-to-last-for-9.1 commitfest (2010-11) started punctually on 2010-11-15.

That means if, while being a team player on all the community efforts, you wanted to develop a major new feature for PostgreSQL 9.1, you had a total of about 20 days to do it. (That is, if you didn't spend several days in early November at PgWest.) And that is within a one-year release cycle.