Merge pull request #6299 from hashicorp/fix6247

add note about key interval to virtualbox docs

website/source/docs/builders/virtualbox-iso.html.md.erb

@@ -335,7 +335,10 @@ all typed in sequence. It is an array only to improve readability within the
 template.
 
 The boot command is sent to the VM through the `VBoxManage` utility in as few
-invocations as possible.
+invocations as possible. We send each character in groups of 25, with a default
+delay of 100ms between groups. The delay alleviates issues with latency and CPU
+contention. If you notice missing keys, you can tune this delay by specifying e.g.
+`PACKER_KEY_INTERVAL=500ms` to wait longer between each group of characters.
 
 <%= partial "partials/builders/boot-command" %>
 

website/source/docs/builders/virtualbox-ovf.html.md.erb

@@ -298,7 +298,10 @@ all typed in sequence. It is an array only to improve readability within the
 template.
 
 The boot command is sent to the VM through the `VBoxManage` utility in as few
-invocations as possible.
+invocations as possible. We send each character in groups of 25, with a default
+delay of 100ms between groups. The delay alleviates issues with latency and CPU
+contention. If you notice missing keys, you can tune this delay by specifying e.g.
+`PACKER_KEY_INTERVAL=500ms` to wait longer between each group of characters.
 
 <%= partial "partials/builders/boot-command" %>