★ Using Socialize to distribute your feed on social networks – FeedBurner Help
As your feed updates throughout the day, FeedBurner picks up your feed and looks for new items. The Socialize service will detect these new items and post up to 5 of them to twitter at a time. Note that the speed with which feed updates can get to FeedBurner will affect this service. To ensure your feed updates in near real time, make sure you ping us immediately after your feed updates and that your blog platform is configured to use PubSubHubub. If none of these options are used for making your feed near real time, the Socialize service will look for and update with any new feed items every 30 minutes.