OkI think I understand your requirements but as I stated Windows
cannot directly control the remote bluetooth speaker, this is because of the intrinsic way that bluetooth works. If Bluetooth is switched on and a bluetooth device is paired then it will automatically connect.
This means that we need to find an alternative control function that Windows can
control the setup - my first technique was to control the audio service, but as you wish to retain the audio on the actual PC in the office we need a different approach.
The only other controllable service involved is the overall bluetooth system, (But as far as I know there is no existing applet to control this such as NirCmd for the audio).
This can, however be controlled by a Batch file that replicates the manual mouse clicks you would normally perform to switch off Bluetooth or any other service, (go into the services applet and select "Stop" against the service involved),
The major issue with this or the audio method is that there is no way to target the remote Bluetooth speaker directly, so the technique will disable the speaker it will also disable all other bluetooth devices
The only way, that I am aware of, to control the switch off ( using programming Basics it would be - IF User forgets AND a reboot occurs), is via a task that does it based on a time trigger It occurs each night at a set time (it can also be used as a manual shortcut on your desktop, which allows you to switch off/on from the office or can be achieved by clicking the bluetooth tile in the notification area, switching back On is also possible by the same methods)
The information to create the batch files needed for Bluetooth service control is contained in the following link
Disable Bluetooth in Windows 10 [Updated]
This would be used to create two batch files (On & Off) that would be used by the original Scheduled tasks in my first post and if needed manually for remote control from the office .
Out of the Box Idea
One other way I have thought of is to control the Power for the Bluetooth speaker, these days there are a lot of remote control automation devices available for use in the home - This could be a simple plug-in timer that switches the wall socket powering the Speaker between two times overnight, or one of the newer fancy WiFi units which can be controlled remotely with a remote control or even the PC.
One system that I used for a long time, was a simple idea - I had the habit of going out to work without small items that I needed (mostly USB devices that I would leave plugged in at home), and need when a got to a job - the cure was a low tech one of a post it note fixed to the inside of my front door
It worked which is all that mattered. I now use my scheduler on the cell phone to give me regular reminders, Have you done this... Have you considered to do ... They are set to occur at regular times as a prompt only