Project management is a critical task during the entire time of the project, in my opinion this should start as early as Sales. As soon as you try to sell something it is important to know whether you already have what you are selling or that it still needs to (partly) developed. As soon as some work is required to handle the customer’s request it is critical to assess how much effort is it and how long it will take.
Selling things you don’t have the time to create or that you are not willing to invest in as it is not considered to be essential for the company is a waste of time. As soon as the project is sold a detailed plan should be created and kept up to date as work goes on. The traditional way to do it is having a project manager that will take care of this, there are often some flaws with this.
The biggest problem is that the project manager will live on his own island and discuss things with the customer without sufficient input from the team. He makes assumptions based on previous projects without knowing the exact details of it. This will then lead to too much work for the specified amount of time and as the deadline comes closer more stress will be put on the team to meet it.
In the end the team will have to meet the deadline set by people above them. But it is impossible to hold someone responsible for something he did not agree too. If you are part of such a team it is essential you try to get involved in the process and give input as soon as possible, but if that fails and you know the deadline is impossible don’t do a lot of overtime just to meet it. This will give the management more reasons to just specify deadline without your input. During the entire project update them with all the work that still needs to be done and your estimation of it all. They will quickly see that there is more work to be done than what they thought. Also tell them you want to be involved when a deadline is set.
Management often is still able to postpone the deadline, and if they only learn the hard way there is nothing in it for you to push yourself to meet the deadline. It will never get better until management hits the wall themselves.