I have two departure times set: one for weekends, one for work week morning. So basically I have one departure time every morning. When my car was left for three days each time, it meant I got home and plugged in on a weekday evening. My car would then miss three scheduled departures due to not being driven, and the fourth day is when I would drive and see the warning. I will have to try reducing the period of inactivity by one day each time to see what the threshold is, but once I get snow tires on I won't have to leave the car in the garage.
Okay, that scenario matches my expectations. I speculate that if you skip two days and drive on the third, you won't see that warning on the fourth morning (and the skip counter resets to 0).