Xenoblade Chronicles if you play through it normally and aren't a completitionist takes almost 50 hours.
It is no doubt one of the best JRPGs of the last gen and yes, it is a very good idea to start it before XCX comes out just so you can get used to how the series is.
[Switch Friend code: 3909-3991-4970]
[Xbox Live: JissuWolfe]
[PSN: Jissu]