In a dental office they would squeeze quite a lot into the tooth trays and have it sit on your teeth for 3 mins or so, much like a fluoride treatment.

At home, put some on your finger and rub it on the front and back of your teeth, let sit for 3 mins.

Rinse it off after that time, no eating or drinking for at least 30 mins after.

So would you use it just before brushing? Or is it better to brush (with a toothbrush), then wait 30 minutes (for the toothpaste fluoride to take effect), and then apply GC Tooth-Mousse?

After brushing, just like a dentist would apply fluoride after a cleaning.

Dentist recommended to apply it on your finger and “brush with your finger”