5 digits is what is returned from the GPS satellite’s NEMA file and what is used by the LocationSensor. It is not possible to achieve centimeter accuracy. Read about how to use the LocationSensor here Using the Location Sensor
The LocationSensor uses the NEMA $GPRMC string to report it’s geocoordinates. The actual data of the $GPRMC string is hidden from the user). The precision is FIVE decimal places and is what the original satellites report. Sorry, you cannot get the accuracy you hope using App Inventor. Instead, program with AndroidStudio that has the libraries necessary to use advanced chip set capabilities.
Is there a way to get a GPS calculation at least each second? Not really. You only get a revised location when the LocationChanged event fires. Since it typically takes 20 seconds for the GPS to revise a satellite fix, updating more frequently than about each 20000 ms produces no practical results. Yes, you can set the LocationChanged event to attempt to trigger every 1000 ms but the new coordinates will not report that fast.
Regards,
Steve