Thought I'd share two tidbits of info re: proctored selftests.
I got back from France a week ago; my partner stayed on an extra week. I tested using iHealth and its proctored service; I did the test right after midnight the day before I would be flying, just to get it out of the way (I was also staying in a private residence where I could hole up if I tested positive, so wanted to know ASAP if I was positive -- fortunately, I was negative).
My partner thought he'd also do a just-after midnight test, this time using the Binax test/eMed service. The problem, as we discovered, is that eMed uses UTC time as the time of the test, which was two hours behind France; thus, the emailed PDF result was dated for 10:30pm the previous day, not 12:30am on the day we needed (see the eMed FAQ for an explanation of UTC and testing time: https://www.emed.com/contact-us). Apparently, had we used the Navica app, the local time would have appeared correctly.
I uploaded the test to United Airlines, and of course it was rejected; my partner used another Binax test in the morning to get the proper date on the result.
Moral of the story is, I guess, use the Navica app, be aware of the UTC time for the date you require, and bring an extra test or two!
Re: iHealth -- it appears that they are "sold out" of the proctored service. There is no explanation on their web page or Twitter account. This has apparently been going on since early May; if you already bought the service, you can still set up appointments. I used mine on May 9.