Here's how the feature works. When you click on the "Refresh All Craigslist Feeds in Background" button, we find all of your Craigslist feeds and schedule them to be refreshed. The scheduled time is a function of how many feeds you have. This way, if you have 1500 Craigslist feeds, we won't blast Craigslist with 1500 requests all at once, which would surely result in our servers getting blocked. So, the more feeds you have, the longer it takes to fetch all of your feeds. Roughtly one feed per second, so if you have 1500 feeds, it will take just under a half hour to update your feeds.
We also restrict how often you can refresh all Craigslist feeds, so clicking that button every 5 minutes won't do anything for you.
Now, some of this functionality may have not worked at the end of last week (2nd November - 9th November) as we still had some servers blocked by Criagslist. As it stands today however (11th November), all of our fetching servers have access to Craigslist.