After a certain amount of experience in life, it's so easy to know how long it takes you to shower, get ready, drive a certain distance, whatever, and plan accordingly. That's why I am always pretty pissed when someone is late regularly without a reason that's out of their hands. It reeks of "Well, I am important, I have many things to do, it's okay for you to wait".
Just start whatever's on your schedule earlier and keep an eye on a clock while you're at it! (I am speaking generally here, not addressing anyone or giving tips)