Hello Jonathan, thanks for your message. Sorry for the delay, there are lots of support questions at the end of the year.
What I understand is that you want to switch on your lights on a calendar event.
It is not possible to link Google Calendar to Hue Essentials at the moment. I added that to the wish list for future development, it seems very interesting.
What you could do instead is use Tasker for this. I am sure that there are Tasker plugins that can trigger tasks on a (Google) calendar event. Hue Essentials has a Tasker plugin to control your lights, so as task action you can use Hue Essentials to switch on a light. See for more information: How do I use Tasker?
Tasker will run on your phone, so your phone needs to be on in order for Tasker to work. If you sign in with Away from Home in Hue Essentials, the tasks will also work when not connected to your local WiFi.
Let me know if you have any questions.