I was thinking of setting up a task with a state of BT Near that loads the app.
Unfortunately, the device doesn't seem to appear in my list of devices available when it's turned on.
https://play.google.com/store/apps/details?id=com.macdom.ble.blescanner
I found a way to get it to work. I installed the linked Bluetooth scanner app which allowed me to get the address to use in the task. Tasker by default scans BT Evey 120 secs and that's how long you clean your teeth for, so hopefully they overlap well. Big question will be if it impacts battery life searching for a hidden BT device.https://play.google.com/store/apps/details?id=com.macdom.ble.blescanner