Jay Leno is staying at NBC… and moving into prime time with a 10 p.m. Monday-Friday show in the fall. Conan O’Brien takes over the Tonight Show at 11:35 p.m. as previously planned. Good for NBC, which keeps Leno, and saves a lot of money by programming a relatively inexpensive talk show instead of five hours of scripted drama. The network can move “Law and Order” and “Law and Order SVU” to 9 p.m. “My Own Worst Enemy” and “Lipstick”, two other 10 p.m. shows, are on the way out, while “ER” is wrapping up its final season. NBC has failed to create a 10 p.m. hit over the past few years, but the Leno move is also an indication that the 10 p.m. hour has lost its luster. Many viewers tape shows and watch them at that hour. For instance, on Thursday night, watch “Grey’s Anatomy”, tape “30 Rock” and “The Office” to watch after “Grey’s”