Hi Dave
You can add a job to any day on the planner, whether it is due or not, but Aworka gives you hints about which jobs you should be doing next, e.g. the jobs are listed in next due order, so if a job is already planned, it will be further down the list. The jobs are also coloured in the list to indicate how late or early they are.
If a job is already planned, but you want to do it earlier, you can drag it to an earlier date rather than adding it again.
You might also find the Highlight option at the top right of the planner useful, to show jobs which are planned in too early or late.
I have debated whether Aworka should do more to prevent you planning jobs too early, etc, but as one of my users said "Aworka let's me control my schedule, not the other way around."
As ever, I'm open to suggestions... maybe I could add an option that would allow Aworka to remove a future job from your planner if is added to an earler date...?