Here is my detailed update that I have been sending to my apple technical assistant who is working with me. I am using Windows 10, iPhone 8 plus with ios 11.3.1, and iTunes 12.7.4.80.
Here is my report for the May 1, 2018 addition of 205 photos in three subdirectories. IT WAS SUCCESSFUL BUT VERY LONG!!! Total time for the sync was 3.90 hours!
2:37 PM backup. Add photos: Ed Retire (25), Retire (45, stanwed (135).
2:43 PM backup finished. Reading photos from Photos (step 5 of 6)
3:19 PM Reading photos from Photos (step 5 of 6)
4:13 PM Reading photos from Photos (step 5 of 6)
4:38 PM Reading photos from Photos (step 5 of 6)
4:58 PM Reading photos from Photos (step 5 of 6)
5:46 PM Reading photos from Photos (step 5 of 6)
6:02 PM Reading photos from Photos (step 5 of 6)
6:28 PM copying X of 1007
6:28 PM waiting for items to be copies
6:30 PM Finished. All on phone.
iTunes bar now reports 8240 photos now on phone. I am assuming this includes camera roll.
Like everyone else I am waiting for apple to figure this out and get a fix. My experience with the problem before I upgraded to the iTunes 80 build was even if I add no photos, the sync times are unacceptably long. I have noted that all folders in the iTunes photocache are re-dated. The thumbnails appear to have the correct dates.