How long does it take your baby to fall asleep for daytime naps?

My son sleeps wonderfully through the night and at bedtime goes down without any struggle. During the day, however, he fights every nap. I only put him down to sleep when I notice the first signs of sleepiness. He then lays in his crib for a good 10-20 minutes. The first 10 minutes he actually cries, not distressed crying, more like irritable crying, then the last 10-5 minutes he chews on his shirt or fingers and talks to himself as he nods off, occasionally crying out when he realizes that he is falling asleep. After all this, he sleeps for about 30-45 minutes. Does your baby have a process for falling asleep for naps?