The "date trick" didn't work for me either. I'm using iPhone 6 with IOS 10.3.3 and setting the date back didn't show any additional photos in "Recently Deleted".
I had 622 MB of wasted space, supposedly used for "Photo Library". I have "iCloud Photo Library" disabled and "My Photo Stram" enabled. Since changing the date didn't help, I went into "Settings -> Photos & Camera" and enabled "iCloud Photo Library" just to see if that made any difference. But apparently it made things even worse since it started increasing the "Photo Library" size (as visible in "Settings->General->Storage & iCloud Usage->Manage Storage->Photos & Camera") in front of my very eyes. It increased from 622 MB to 1,31 GB in a span of 1 or 2 minutes. The "Photos" app still shows everything at 0 (Camera Roll, Recently Deleted, Photo Stream).
I then turned "iCloud Photo Library" back OFF and toggled the "My Photo Stream" setting as well, but nothing changed. So now I'm at 1,31 GB of wasted space which I can't recover.
The scary thing is that this issue apparently exists at least since 2014 and Apple still didn't fix it. I'm guessing people don't even know they have it until their phone starts showing the "Low memory" warnings. That's how it was on my iPhone.