Howto trigger BEFORE an event with Google Calendar Scheduler? (Engine block heater)


Winter is coming and I’m trying to make a smart temperature based car engine block heater rule.
At the moment I use Google Calendar Scheduler to set the time when I want the block heater to start. It works well, is flexible and it’s easy to move or add an extra start time when you use the car on other times than the usual go-to-work time. It’s also convenient for multiple users to add times in a shared calendar.
The downside with this approach is that I have to manually decide when the heater should start, based on what temperature I think it will be at that day.

What I would like to achieve instead is that I set my time of departure in the calendar and the rule starts the heater X minutes before that. The colder outside, the longer time with heater on.

But how to I get OpenHAB2 to react 3 hours BEFORE an event in the calendar? Is this even possible with the Google Calendar Scheduler? Or by any other method?