This will vary from person to person, and if you are running Windows with frequent feature updates like Windows 10 and you want to try new features yourself, the best time to do so is immediately after purchasing a computer. Data will not be lost, but other data and software have not been installed, so the update will be faster.
If you are not interested in updating, Or if you have internet problems, it is best to turn off Windows Update. The shop can ask a technician for help, or if you right-click This PC (My Computer) and search for Windows Update in Manage – Service & Applications – Services and disable it, the update will not work automatically.