Calculate the time spend inside area (Time-aware geofencing)

Hello friendly FME Community!

I'm trying to implement a GeoFencing service which will calculate the time spent by vehicles in particular areas.

In short, I have a set of points (with timestamps) and set of polygons (geofences) against which I want to calculate how long these points were inside these polygons. 

I did make a workspace which does this using SpatialFilter (which identifies if points were inside polygons) StatisticsCalculator which calculates min and max timestamps and DateTimeCalculator which calculates the interval between this min and max timestamps.

The problem is that vehicle can move out of all polygons and then get back which will distort the calculation as the period that vehicle was outside the polygon will be included because last timestamp will be inside the polygon.

Is there any trick or technique in FME which allows to follow up these gaps and exclude them from calculation described above?

Thank you in advance for any suggestions!