A lie is the intentional telling of a falsehood. God gave man the power of speech that he may express what is in his mind, and to abuse this power by telling a lie is both unreasonable and sinful. Now one lie does not make a man a liar, but if someone has a bad habit of lying on a consistent basis, we can justly say that man is a liar.
So is your boss a liar? Well, if he habitually and intentionally gives you false deadlines, yes. Your boss may attempt to justify his vice as a means of increasing productivity, but his excuses don’t much matter. The ends never justify the means. The fact is that any habitual teller of falsehoods is a liar.
If the project is due on Friday, justice and truth demands that your boss tell you the project is due on Friday. If your boss tells you the project is due on Thursday, he has told a lie. No one should work for a liar, so if your boss fits this description, you need to find a new boss.