Leave the tab open when you put your PC to sleep, if you're on PC and you put it to sleep. The offline earnings won't calculate if you put it to sleep.
But truthfully, not much can be skipped with offline earnings. It might seem like it, but it's not that powerful because when you're playing, the LOREDs are leveling up which doubles their output. You could have surpassed offline earnings in a short time!
But I don't see a reason why I couldn't add an option to disable offline earnings in 3.0.0!