In fiction, things have to happen quickly. Many movies and TV shows show events that happen over the course of long periods of time; years, in some cases; but for the purposes of getting everything done, that time has to be condensed. Otherwise we'd all be sat in cinemas for months on end! Real-time works of fiction tend to be fairly unique, which was one of the appeals of Kiefer Sutherland's '24'.
Although it wasn't possible to make all of 'Saving Private Ryan' in real-time, Spielberg wanted the audience to get a sense of the ebb and flow of a real battle, and so as many of the sequences as possible play out in real-time as possible. Because of that, when Paul Giamatti's character announces that 'the streets have been quiet for around 45 minutes', exactly 45 minutes of the film have elapsed.