There is a Police Dash Cam video of the parking lot of Sandy Hook. I show the official timeline as written out by the Police of what happened and when.
The official timeline says they began evacuating the children at 9:58 AM from the school and walking them across the parking lot to the firehouse.
Here is the State Police site to view the Police Dash Cam video.
There are different times going to 10:03 AM of masses of children being evacuated at one time from the school and going across the lot.
The dash cam video has a few redacted seconds, but they are only seconds of time and there would be no way of getting the children across the lot in that amount of time.
Watch the Police Dash Cam showing the parking lot compared to the official Timeline:
http://sherriequestioningall.blogspot.com/2014/03/sandy-hook-police-official-timeline.html