I manage around 40 Dell PCs of different ages and have updated them with each Win 10 upgrade from the start. This 1903 is the slowest yet and hangs around the 85%+ stage for ages and can take 15-30 minutes to reach 100% from the 85% point and then the long blue screen final stage. So if you are doing this upgrade be prepared for it to take an hour or two. I've been doing them overnight to avoid impacting the users.