B&J were on West Florissant Avenue for ten minutes

A business called Shopping Center Services (SCS) was located at 9292 West Florissant Avenue, at the southeast corner of the intersection of West Florissant Avenue and Canfield Drive. According to the Investigative Report (pages 167-168) SCS had a system of closed-circuit television (CCTV) cameras, and three of the cameras were pointed at that corner's sidewalks.

-- Camera 11 was pointed north, toward Canfield Drive.

-- Camera 2 was pointed northwest, toward the intersection.

-- Camera 9 was pointed south, toward West Florissant Avenue.

The following images were taken from Google Maps.

Location of Shopping Center Services at the intersection of
West Florissant Avenue and Canfield Drive
in Ferguson, Missouri

Satellite view of Shopping Center Services at the intersection of
West Florissant Avenue and Canfield Drive
in Ferguson, Missouri

The street view can be seen on this webpage.

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The SCS CCTV system's clock ran 18 minutes ahead of the Ferguson Police Department's dispatch clock. This difference can be calculated because

* Camera 11 filmed Police Officer McDonald passing by SCS on Canfield Drive toward the shooting location at 12:20:07 according to the SCS CCTV clock

* The police events log indicates that Police Officer McDonald passed SCS at about 12:02:07, according to the police dispatch clock.

Correcting all the SCS camera times by those 18 minutes, Brown and Johnson were filmed at that corner at the following times.

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Walking to the store:

11:44:40 = Brown and Johnson are walking on Canfield Drive's north sidewalk toward West Florissant Avenue -- Camera 11 at 12:02:40

11:45:28 = Brown and Johnson are crossing to Canfield Drive's south sidewalk -- Camera 11 at 12:03:28

11:45:57 = Brown and Johnson are turning the corner and are beginning to walk south on West Florissant Avenue's east sidewalk -- Camera 2 at 12:03:57

11:47:24 = Brown and Johnson are continuing to walk south -- Camera 9 at 12:05:24

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Walking from the store:

11:55:22 = Brown and Johnson are walking north on West Florissant Avenue's east sidewalk -- Camera 9 at 12:13:22

11:55:59 = Brown and Johnson are turning the corner east onto Canfield Drive -- Camera 2 at 12:13:59

11:56:33 = Brown and Johnson are walking on Canfield Drive -- Camera 11 at 12:14:33

11:56:53 = Brown and Johnson begin passing a different fence and so disappear from the camera's view -- Camera 11 at 12:14:53

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This image shows the beginning of the different fence that blocked the camera's view.

The thicker, darker line is a fence that blocked the camera's view
of Brown and Johnson as they continued walking east on
Canfield Drive. 

In the above list, two times are highlighted in red -- 11:45:57 and 11:55:59. The first time in the moment when Brown and Johnson turned onto West Florissant Avenue on their way to the store, and the second times is the moment when they turned off of West Florissant Avenue on their way from the store. The difference between the two times is about ten minutes.

This ten minutes includes the time -- about one minute and 21 seconds -- that they spent on the store's premises.