Since it's rare to actually pick up the phone and call someone after a date, the "three day rule" has died—but this also opens up a lot of new questions when it comes to time frames and relationships, including "When to text back?"
If you're at all curious about the texting habits of your contacts, the Texty Time app for Android is one that will break down all the data for you. The app provides a rundown on the number of messages, words and the average minutes before you get a reply, and charts this information over time. With enough use, you'll even be able to see records for the past year.
With this kind of data at your fingertips, it should be easy to see when someone you like may be too much of a clinger, or not interested enough.