In my experience, the best way to get a high-quality software product is to take your time, not crunch to some deadline. On one project I led, after a couple of months we realised that the feature goals (ALL of them) and the performance goals (also ALL of them, in this case ALL of the iPads back to the first-gen, single core 2010 one) were incompatible.
We talked to the customer, worked out achievable goals with a new timeline, and set to work with a new idea based on what we had found was possible. We went from infrequently running Instruments (the Apple performance analysis tool) to daily, then every merge, then every proposed change. If a change led to a regression, find another change. Customers were disappointed that the thing came out later than they originally thought, but it was still well-received and well-reviewed.
At the last release candidate, we had two known problems. Very infrequently sound would stop playing back, which with Apple’s DTS we isolated to an OS bug. After around 12 hours of uptime (in an iPad app, remember!) there was a chance of a crash, which with DTS we found to be due to calling an animation API in a way consistent with the documentation but inconsistent with the API’s actual expectations. We managed to fix that one before going live on the App Store.
On the other hand, projects I’ve worked on that had crunch times, weekend/evening working, and increased pressure to deliver from management ended up in a worse state. They were still late, but they tended to be even later and lower quality as developers who were under pressure to fix their bugs introduced other bugs by cutting corners. And everybody got upset and angry with everybody else, desperate to find a reason why the late project wasn’t my fault alone.
In one death march project, my first software project which was planned as a three month waterfall and took two years to deliver, we spent a lot of time shovelling bugs in at a faster rate than we were fixing them. On another, an angry product manager demanded that I fix bugs live in a handover meeting to another developer, without access to any test devices, then gave the resulting build to a customer…who of course discovered another, worse bug that had been introduced.
If you want good software, you have to sleep on it, and let everybody else sleep on it.