When you receive Tweets or retweets from DataSift, you receive them in real-time, as they are created. If you would like to filter for Tweets or retweets created in the past, you will need access to DataSift Historics.
To filter for just Tweets, and not retweets, you will want to filter on the twitter.* targets, such as twitter.text. A full list of available targets you can filter on is documented at dev.datasift.com/docs/targets/twitter