Depends what you're using your QT for. Is it for treating a ill fish or just getting a new fish?
For sick fishes, if you put any LR
or live sand into the QT and depending on the chemicals you put in there, you can't put the rocks back in your DT. I know for sure copper shouldn't be used with LR
If its just for quarantining a new fish, then sure you can move the LR
back and forth. People usually leave an extra sponge filter to build up a bacteria's on there and when needed, they just throw the sponge filter into the DT. Just an advice for future use.
The amount of LR
you use is probably 1 lb per gallon to be safe.