Hi Alvaro,
Sorry that you’re having that issue, please do the following, first try increasing your PHP Maximum Execution Time as currently it only stands at 30s
, you can follow the guide here or ask assistance on your hosting support on how to effectively increase PHP Maximum Execution Time.
Another thing, I notice that your site is under Cloudflare, please purge the Cloudflare cache and put it on development mode for awhile.
Purging cached resources from Cloudflare
If the issue persists, please deactivate all your plugins (except Cornerstone) for awhile and try importing demo again.
Let us know how it goes,
Cheers!