You're constantly annoyed by the fact that plants or duties take forever to complete. I don't recommend using the Airplane Mode cheat or whatever it's called, but do it as you like.
However, you can get your sims to plant while you're sleeping or at school. I do this everyday when I'm sleeping and I do it before I leave for school.
School takes about 8 hours, so I suggest planting Garlic, Beans, and/or Onions.
Overall, if you know how long you sleep or for how long you'll be in school, take that time to have your sims planting and you'll have lots of money in no time.
It's like being paid for sleeping and/or learning