Right now our native Google Calendar integration is push only, i.e. it will allow you to create entries in a calendar based on something like an invoice due date or end of year deadline. You can’t pull events from Google Calendar and use their respective dates to bind against invoices/estimates.
This is something that is outside the scope of what QuickFile seeks to achieve. There are so many different applications and types of businesses using QF we can only really support a handful of popular routines/apps, for everything else there’s the API.
Also Zapier may allow you to solve this, we will likely start exploring this soon.