Hi,
I'm still using iPhone 6s, so I can't create a HVEC file to test with it and see what import methods work with it. According to the literature it is an improved format over the commonly used H.264 codec. Being relatively new to the market, consumers are still leaning how to work with it.
Your profile indicates that you are using Sierra. Be sure to update to High Sierra, that is the operating system designed to work with HVEC together with iMovie 10.1.8.
Also, your mid-2010 Mac probably does not have the hardware to work with HEVC. From what I have read, you might need a 2017 Mac. But I will defer to others on this forum who might already be working with HEVC on older computers. I just haven't seen enough feedback yet from users about HEVC to comment definitively.
As long as you are able to export from Photos, at least you can work with HEVC, if you can live with the time stamp issue. You might also convert to another format. I think that the freedownload, Handbrake, will do that. Of course, that would mean losing whatever advantage that HEVC has for you.
-- Rich