Parkinson's Law on Wikipedia
Work expands so as to fill the time available for its completion.
In its original context, this Law was based on studies of bureaucracies. It may be pessimistically applied to software development initiatives, the theory being that teams will be inefficient until deadlines near, then rush to complete work by the deadline, thus making the actual deadline somewhat arbitrary.
If this law were combined with Hofstadter's Law, an even more pessimistic viewpoint is reached - work will expand to fill the time available for its completion and still take longer than expected.
See also: Hofstadter's Law