ENGLEWOOD, Colo. — Tim Tebow looked at his options, looked some more, and finally decided to squeeze it to his receiver in the corner of the end zone.

The window was closed. Rookie cornerback Perrish Cox easily intercepted Tebow's pass during the red-zone drill in passing camp practice Thursday.

Even though Tebow was promoted, taking third-string quarterback snaps after being the fourth-stringer in every other open practice this month, the first-round pick still has a long way to develop.

"I don't know if it's moving faster than I anticipated," Tebow said. "I know it's moving fast though."

So far, Tebow's limited practice repetitions have looked about the same. He shows good physical skills when he throws the ball. His arm strength is fine ("He can throw the ball pretty well, he has a great arm," cornerback Champ Bailey said) and has usually thrown with pretty good accuracy.

But the mental part of the game has admittedly been a challenge. That has led to many indecisive moments, with plenty of short passes to avoid making mistakes.

"That's the hardest part of being a rookie is your thinking," Tebow said. "You're constantly thinking, 'What am I doing here? What if they do this? How do I do this?' It's studying so much where all of that is second nature where you just go and play, and play fast."

Tebow said he is getting more comfortable every day, and the complicated looks thrown at him by the defense are getting easier to decipher. He didn't think the physical speed of the NFL was that overwhelming, because he played in the Southeastern Conference, which has plenty of talented athletes. But he has been struck by the ease in which players move between coverages, quickly disguising the defense to confuse him.

The coaching staff understands that rookies are going to struggle at times to learn complicated schemes, whether they play offense or defense.

"The rookies, for example, right now, they're out there and their heads are just spinning," Broncos coach Josh McDaniels said, although he wasn't discussing Tebow specifically. "And when your head is spinning you can't play football the way you know you can play football because it's hard to go as fast as you can."

Although it seems every move he makes now is dissected, the spotlight will be even more intense during training camp and the preseason.

The good news for the Broncos is Tebow's work ethic will help him get up to speed quicker than many other young players. Tebow's attitude is one of the reasons the Broncos loved him coming into the draft.

"I knew it was going to be tough," Tebow said. "I've got to come out here with a great attitude and work hard every day, and do what they tell me, and that's how I'm going about it."