Sometimes on a project, we focus on an intermediate milestone in the project, such as Beta, or first performance test, or early ship. The project team works like dogs to make that intermediate milestone. Then, there's still the rest of the project. Uh oh. Now you're starting to cross the desert. (Thanks to Jack Nevison of Oak Associates for that great metaphor.)
In our house remodel last year, we focused on the upstairs bathroom completion. The bathroom was completed in February. We had about 8 weeks of work remaining. The project completed in September. (!!) The project completion was so late because everyone had juggled previous commitments to meet the intermediate milestone and worked too many hours on our project, ignoring the rest of the contractor's work. It took forever to complete our work.
This happens on software projects too, sometimes with even more dramatic results. On one project, the team worked 10-12 hours a day, 6 or 7 days a week for three months, to make a Beta release. We did. Everyone took the next week off, leaving the tech support people fielding calls. We came back to work, somewhat refreshed. However, we had significant work to complete before we could release. We were still exhausted and burnt out. And, now that the customers had the product, we had even more pressure to complete the project.
Crossing the desert hurts. It hurts the people and frequently hurts the project. If you have to focus on an intermediate milestone, pace your project team. Don't let the project team start with overtime before the very end (last week or two) of the complete project. Early overtime == later project completion.
You won't find an oasis. So don't cross the desert.