You really don't understand how pacing works do you? The first day of the war lasted 22 chapters. The first night lasted 9 chapters. The second day of the war lasted 42 chapters. The second night has been going on for 60 chapters, and its still going on. Time has little no relevance when it comes to manga chapters, especially if the chapter is action heavy. A fight could last 10 chapters, but as long as its more action than dialogue, in real time that 10 chapter fight could have only lasted 20 minutes. The 15-minute thing was introduced only to build suspense so that the characters could have a fighting chance of stopping the jutsu, while keeping the tension because they know they have a small window of opportunity. When you watch a movie and the bad guy gives a 5-minute warning/leeway, do you really think everything you watch after that is really 5 minutes? No, its more like 20, but in the movie time has moved 5 minutes. Same idea here.