First issue I find is that I don't have enough space on my phone. I just got back from vacation so I am downloading pics and videos to clear up space.
Once clearing off enough space (I had over 2.5GB free), the download started working. Actual time to download the files was about 30 minutes but I have a very good wifi connection to a internet connection of over 2GB/sec at work. Obviously, I didn't come close to those speeds due to many factors. It took a long time for the phone to 'prepare to install' and the 10-15 minutes for the phone to restart and install the new OS is running past 20 minutes now and I am still at 75%. Total time so far is 1 hour and 10 minutes and counting.
And 2 hours later (almost to the minute) all is updated, even my apps that needed updating. Everything seems to be operating smoothly. I had a phone with the Windows 10 Preview so I cannot wait to use a lot of the features I have been waiting to get back with my latest Lumia 735.