I would agree that seeing the kid run is more important than the time. So, I can live with that as an assessment. The tall kid that was fairly fast had a long stride but his turnover could have been faster. The smallest kid had great turnover but no stride length, however, he got the most out of what he had. And their second runs looked identical to the first.
The main issue I saw was with the big, somewhat heavy kid. His first run looked ok, though not fast. His second timed run was dramatically slower, indicating he was out of shape. But, the eyeball test sort of showed that anyway. What that tells me is that if he hits a double, you need to call time and have a conference with your next batter to give him a rest. And it's going to take another double to get him home.