Amazon has just pushed out a new firmware update for any Kindle made in the past five years. In-book search now includes results from your notes and highlights and a clock now appears at the top of the screen when you are reading a book. If you are not a fan of the time, or merely groan to yourself that you have been reading for nine hours straight, you can disable it in the settings menu.
Update 5.9.4 should be pushed out to all Kindles within the next few days and it will will automatically install it when the device is in sleep mode. You will likely notice a reboot next time you use it, along with a notification window that advises you of the new changes.