Depending on the machine and the flavor of the previous system, it has taken anywhere from 90 minutes to 4 hours. The fastest was from W7 Pro using as flash drive.

The tool gives you the option of a download to either a DVD or a USB device. Personally, I like the flash drive if I am not installing directly.

The worst error I have made was not having the machine hooked to the internet while doing the upgrade. That cost me the time to revert to W7, then reinstall W10 Pro. I do like the feature that the media automatically selects the version you get for the upgrade.