They don't expect you to shave in 30 seconds. During your first few weeks of basic training/boot camp, the instructors will order you to do things they KNOW you can't do. It's to put pressure on you and see how you react. On a normal day in training, you'll get more than 30 seconds, although when I went through basic some people would get up 10-15 minutes early to start hygiene. When you finish training and go to your permanent duty station you have as much time as you want to do personal hygiene.