sylvainkalache on "[Plugin: Tumblr Importer] In progress...."

I found the solution.

The author of the plugin says you have to generate activity on your website, by this he means on your Wordpress blog. But the actual thing that you want to do is trigger wp-cron, which is something that Wordpress uses to trigger schedule actions.

So you need to access this from your browser: http://nameofyourblog.com/wp-cron.php
And the import process should happen.

source: http://bitswapping.com/2010/10/using-cron-to-trigger-wp-cron-php/