I doubt that's gonna work or we'd all start 2 day productions right before the time runs out
That's exactly why I wonder. It would not be fair to start a production and pay double for it, but then end up with the regular amount of produced goods. Imo this isn't too different from using a boost spell after your long production is over, but before collecting it, and boosting that production.
The more fair way to handle this would have been if all productions that were started when the boost was released got boosted also. This way we would get "free" double production for them, but would have also double cost for normal productions at the end, which would balance things out. And now the logic suggests the other way - to have double production for the double recourses payed regardless of if the boost is still active.
That's why I ask for more info and some sort of clarification.