To prevent spoilers, this walkthrough will not list any details of any cutscenes.
The game auto-saves constantly so you never need to worry about putting it down and picking it back up later if necessary. Assuming you don't skip any cutscenes, it takes about four hours start to finish, though your mileage will vary based on how quickly you succeed at the gameplay objectives. Still, Longshot doesn't take too long to complete. There are no rewards for Franchise or other game modes, so if you bought Madden purely for that or simple online competition, it's likely you can skip Longshot mode. If nothing else, successfully completing it will reward you with strong cards for Madden Ultimate Team. Speaking of rewards, Even veterans of the Madden franchise should give Longshot a go.