I cropped the area of the sequenced photos in order to isolate the egress of Mercury. The first image here (upper left) was taken at 18:01:34 UT, and the last images was taken at 18:04:06.

Image 477 shows the beginning of the black drop effect at 18:02:33 closest to C3, and is impossible to detect on the images between 18:03:58 (image 490) and 18:04:03 (image 491), which indicates about a 90 second transition. The predictions state that C3 to C4 lasts about 101 seconds, but from the images shown here, I find that the duration was 87 seconds, and looking over images that Glenn Snider has posted http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/TOM2019/TOM2019.html), the duration was about 90 seconds, so why the 11+/- second difference?

I am not sure why there is a discrepancy in time between my images and Glenn's. I did forget to reset the times for my camera, but matched it with the UTC time on my cell phone and it was 4m 03s off, so I updated all the times on my images to be the correct time. I have the start of C3 at 18:02:33, Glenn shows 18:02:59, and C4 I have at 18:04:00, and Glenn indicates 18:04:28, so Glenn's timings appear to be 26 seconds (for C3)and 28 seconds (for C4) ahead of mine. I can see there being trivial differences in the timings, especially when there are gaps in the times, but nearly a half minute off. I will contact Glenn to see if he has an idea about the differences.

(Sequenced_473_to_492_Time_Tags)