Complete noob to developer mode extensions and I'm hoping someone can help me out.

I have a domain pc I will be using to display an internal company web page using Chrome.
The internal web page is set as the default homepage.
No keyboard or mouse will be connected to the pc.

I need the page to update every 5 minutes without any user intervention.

I found an extension named Auto Refresh Plus created by AddonCrop (addoncrop.com/auto-refresh-plus), installed it in developer mode, and it is exactly what I need.

If I close Chrome and then re-open it, I get a message which says "Disable developer mode extensions. Extensions running in developer mode... etc, etc.)
I click cancel on the warning message and all is well until any subsequent reloads of Chrome occur.
The message occurs regardless if developer mode is enabled or not.
From what I understand, this is because the developer hasn't published the extension in the store.

Is there any way I can make this extension usable internally "without" the developer mode extension warning appearing?

I don't foresee the need for any additional options or updates to this particular extension in my particular case.
I was able to pack the extension and create the .crx and .pem files but from this point I'm not sure what to do next.

PC is Windows 7 Enterprise
Chrome ver 45.0.2454.85