Rabbi Eliezer says one can say shema until the end of the first watch. How many watches were there? Three or four? What are signs of each watch? Rabbi Yosi went into a ruin and prayed. Eliyahu Hanavi rebukes him for doing that. What are the three reasons why people can't go into a ruin? Did King David wake up at midnight? Or before? How did he know even when midnight was if even Moshe Rabeinu didn't know?