I have actually heard that some people WERE able to convert TS meals to QS meals through the concierge desk at their resorts. I would not go expecting to be able to do this, but some have been able to since it actually does not lose Disney any money. Of course the other way around (QS to TS) would never be allowed, but going from TS to Qs has been. As the other poster said though, you could easily just to 2 TS on another day and use 2 QS one day. There is no set credits you have to use per day, you can spread them around to fit your itinerary.