Hi.
Import demo doesn’t mean that you need to import all the images. It depend on your hosting max_execution_time.
If it to low (lower than 256MB) please uncheck the box “Download and import file” that you won’t import the product images. But you will replace it by your product images later, so it doesn’t matter.
Other way, contact to your hosting provider ask them to improve your max_execution_time.
Glad you make it Augusto Murri.
Thanks.