He was working on it at 2.5, but I would say he really got it for the most part around 3 to 3.5.

I remember the night my mother died, when he was 2.5, he got me up in the middle of the night because he was hungry--it had been a rough day and he hadn't eaten much. I was making him some chicken nuggets and he looked at the clock and said "3:10." I looked at the clock, and it was actually 2:15--which you might notice looks pretty much like 3:10! He was kind of hit or miss at that point, but it wasn't much longer before he had it down pat.