The data that I downloaded and were written to the USB drive were the same number of files you're showing, 19656. My memory is a little fuzzy, but after the files were downloaded, it took about 2 hours or so to write the files to the USB flash drive ("Programming USB Stick"). Note that in the screenshot below, the remaining time of 37 minutes is just for the Airport Plates. I never saw a "Remaining Time" as long as your pic is showing. The USB drive I have is a SanDisk Ultra 32GB 3.0 flash drive. A 2.0 USB flash drive would take a lot longer to write the files to compared to a 3.0 drive.
Al-in-all, the whole process seemed to take as long as it did when I was using the Seattle Avionics Data Manager running on an iMac using Parallels with Windows 10 or 11.
Update: I wrote the files to a second SanDisk Ultra 32GB 3.0 flash drive ("Program USB stick"), and it took about 1:05 to complete for that part of the operation. So the 2 hour estimate given above may not be accurate, either since I wasn't paying much attention at the time, or the files may already have been unpacked from the first time so just needed to be copied to the drive the second time.