I haven't really read up on it but I think it is connected to PayPal or if you create a label thru eBay. Then eBay knows when you have shipped (or said you shipped) the item because that info is electronically submitted back to them. Ebay does not have to wait for feedback on the shipping.
You can adjust your ship out time on eBay from 3 business days, 5 days or whatever. Then I think if you ship within the time frame you stated in your posting, the shipping star rating kicks in.
From eBay
http://pages.ebay.com/help/feedback/detailed-seller-ratings.html"If the seller met specific shipping time requirements, the seller will automatically receive a 5-star shipping time detailed seller rating and you won't be able to provide a rating for this category.
Note: If we determine at a later date that the seller met the requirements for an automatic 5-star shipping time rating, we may adjust the rating to 5 stars."