Grab AVIDemux and create a 20 minute video by appending the 10 minute video to itself and saving.http://avidemux.sour...ge.net/download.html
Or you can use ffmpeg to concat the video:
ffmpeg -i "concat:input1.mp4|input1.mp4" -c copy output.mp4
If you've got access to Linux, (or use WSL), then you can also try untrunc
BTW, it mentions that if the 'good' sample video was from the same device/source as the 'bad' video, then you'll have a higher degree of success.