For offline/single player you don't have as many gameplay options. There are 3 specific sets of games types for single player:
1--Training:
X-Wing, Speeder Bike Chase, Darth Vader, AT-ST, and Snowspeeder
2--Battles:
Fight AI on each 4 planets
Hero Battles on each 4 planets
3--Survival:
Survive 15 waves on each 4 planets
Each one gives credits based off the level of difficulty you complete, Survival is the longest lasting about 20-30 minutes to complete
So there's maybe 3 hours of single player gameplay if you do everything once. And all of those can be done split-screen. I think if you're offline then you probably don't earn credits which are used to buy unlocks for your multiplayer character.