Snapchat is an image messaging and multimedia mobile application created by Evan Spiegel, Bobby Murphy, and Reggie Brown, former students at Stanford University, and developed by Snap Inc., originally Snapchat Inc. One of the principal concepts of Snapchat is that pictures and messages are only available for a short time before they become inaccessible.
Content on Snapchat doesn't stay forever -- your friends see the photos and videos (but can't save them) and then the content is automatically deleted. The service is very popular with younger users, and some adult parents of those younger users.
This is what is meant by "ten-second chunks". A "chunk" is a block or large, discrete piece of something, in this case of time. Content on Snapchat only exists for this brief period of time, before it is gone. If you followed this particular fictional user Lydia Bennet, you would get to experience her life -- but only for short periods each time.