When an iOS device model is erased for the first time, the whole erasure process consists of two parts:

1. Download the latest firmware version for the device from Apple servers (can take some time if there's a lot of traffic on Apple servers).
2. Erase the device (takes approximately 10 minutes).

Some information about firmware downloading:

• If the firmware image for the particular iOS device model does not exist on the computer, it has to be downloaded from Apple servers before the actual erasure starts.
• If the firmware image for the model already exists on the computer, it is not downloaded again.
• When the firmware is downloaded, there is text "Loading firmware" in the user interface with the downloaded percentage
• Only one firmware file can be downloaded at a time. Other devices will wait for the download to finish. “Loading firmware” text without any percentage will be shown for the devices that are waiting.
• It can take some time to download firmware files because they are quite big (~2GB) and there can be a lot of traffic at the Apple servers.

It is also possible to download the firmware images on one computer, export them and import to other computers. This way all the erasure computers don't have to download firmware images. Exporting/importing can be done from Blancco 5 Mobile Settings for iOS: use the export button to export firmware images to USB stick and then use the import button on another computer to import them.