E: Unable to locate package ros-lunar-desktop-full

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Currently trying to install ROS Lunar on a clean Raspbian Stretch as per http://wiki.ros.org/lunar/Installatio... with this problem. I've done sudo apt-get update and returned with

Get:1 http://mirrordirector.raspbian.org/raspbian stretch InRelease [15.0 kB]
Hit:2 http://archive.raspberrypi.org/debian stretch InRelease                  
Get:3 http://packages.ros.org/ros/ubuntu stretch InRelease [4,008 B]           
Get:4 http://64.91.227.57/repos/rospbian wheezy InRelease [2,097 B]            
Get:5 http://mirrordirector.raspbian.org/raspbian stretch/main armhf Packages [11.7 MB]
Get:6 http://packages.ros.org/ros/ubuntu stretch/main armhf Packages [5,217 B]
Ign:4 http://64.91.227.57/repos/rospbian wheezy InRelease                      
Fetched 11.7 MB in 42s (275 kB/s)                                              
Error: Timeout was reached
Reading package lists... Done
W: GPG error: http://64.91.227.57/repos/rospbian wheezy InRelease: The following signatures were invalid: F57F2D123C1CB06171E8519AEDFBE3695B93BD6A
W: The repository 'http://64.91.227.57/repos/rospbian wheezy InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

followed by

$ sudo apt-get install ros-lunar-desktop-full
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package ros-lunar-desktop-full

I also tried ros-lunar-desktop and got equivalent message.

What have I done wrong?