I have Plantera-DX for the Nintendo Switch, and have noticed a significant decrease in the income when offline.
I have 70 helpers, 61 plots, everything full. My Fertilizer is at 14, my alarm clocks are also at 15, and so I would believe that my helpers are supposed to work for 15 hours after I get offline.
I check nightly to see how they're doing, and typically it says they've made between 24-30 million. This is remarkably low.
When I am in the game (ie. not paused) and I am idling (not helping pick things up in any way), I earn about 200,000/minute (closer to 240,000, but this makes the math easier). This isn't just a fast or slow idle period, it's the average of 30 minutes or so of play time. This equates to about 1 million every 5 minutes, or 20 million/hour (not day), or 300 million/15 hours.
Because I didn't contribute to collection in any way, I figured that this was just how fast the helpers would work. The game or help menus also didn't mention that the helpers would work slower while you're away.
If they do slow down, I think I might advance quicker by keeping the game open, plugged into the charger, and forgetting about it for a while.
Do they slow down? If so, how much?