As a software engineer, the trick is to never tell them it takes four weeks, you promise 5 weeks, procrastinate for 4, and do it in 2, blaming the extra on software being hard. Most execs understand that, and only being a week late is pretty good (my boss adds 2 weeks to all my estimates for his own reporting).

It's a subtle art that most contractors have perfected. Some even deliver on-time, but that's dangerous because the exec might catch on (software is never on-time).