Although I haven’t started working in industry yet, I want to add a little to the Gantt chart “margin of error”. You need to have concrete goals for end dates for aspects of the project. You also need to do your best to get stuff done by those deadlines. You can’t allow too much time to be built in as a margin. Let’s say something ships late. Going off of past knowledge in how long things may take to ship, you would add a specific amount of days as a safety margin. You can’t just say “This part of the project will take 5 days, let’s add another two or three to be safe”. Those small additions add up. Knowing that you have those extra days may not incentivize you as much to finish early or on time as not having them. You can finish early, and you can have delays that have to be accounted for. I don’t believe having extra days added “just in case” is a good idea. If things happen and your dates need to shift, that’s life, but starting out with the idea that you’re going to need an unnecessary amount of time may be a self-fulfilling prophecy.