Perhaps the answer is a 24 hour queue. E.g. you can only add something to your queue if your existing queue doesn't already take you past 24 hours of crafting. The problem with this is the efficiencies which mean you can't actually determine exact crafting times. In principal a 24 hour queue would be ok though. I still believe it is an un-needed feature though and Dev time is better spent elsewhere.
You could work it out something like:
You have 70 skill in longswords
You make 45. You can queue your extra 50% efficiency at another hour on a different item. So if next hour you wish to produce 40 skill Knightly Heater Shields you can craft 20 of those.
And of course since it's a queue you could queue, X work hours worth of gear, and then revert to some default.
