Well, canon already established the war as having lasted from 2156-2160, so they didn't really have much a choice when it came to how long the war lasted.
No, it didn't. The Star Trek Chronology
listed those as conjectural
dates for the Earth-Romulan War, but there's absolutely nothing in canon that specifies those dates, unless you count the illegible screen graphic text Mike Sussman wrote for "In a Mirror, Darkly, Part II." And we know that's actually not
binding on the novels, since the novels have the war beginning in 2155, not '56.