I can time in Quake due repetition from years (i actually studied the timings so I dont have to do any mental processing). Im uncapable of doing 35+35 without focusing. My math side of the brain is absolutely shit, yet i can time 2 items by the second in Quake. I also have to repeat the times constantly or I forget 2 seconds later.
I was once at a LAN and we watched a movie after having played Quake for a day and a half. I was half asleep when I saw a cab pulling over in the movie and thought to myself, "this is the right time to fire a rocket if I want to hit the cab."