Imported GoPro Hero4 time-lapse from bike ride does not sync with GPS data in VIRB Edit
A way to solve this is to first losslessly change the frame rate of the GoPro video to 1 frame/sec, which changes it from 4 minutes to real time (96 minutes).

This answer explains how to extract the raw bitstream from the GoPro video using ffmpeg:

ffmpeg -y -i gopro.mp4 -c copy -f h264 gopro_raw.h264


.. and then remux it with a 1 frame/sec frame rate:

ffmpeg -y -r 1 -i gopro_raw.h264 -c copy gopro_remuxed.mp4


Import the remuxed file into VIRB Edit [VE], add the GPX file and add some G-Metrix gauges.  Finally speed it up again in VE.

VE can only speed up 800%, so the video has to be re-imported* after the initial export.  Speed it up and export again to come back to the original 4 minute length.  Not ideal, but it works.

* I actually had to use iMovie in the second step, since VE kept crashing