The rule of thumb is to wait until you see new growth.
There is no way you can transplant a rose, young or older, without damaging the feeder roots. The first thing the rose will do is grow new feeder roots. It will use the starches and sugars already in the top growth to provide the energy to grow the new roots.
When you see new top growth, that tells you the root system is working and ready to perform it's natural function for the plant. Saturate the plant the day before feeding and use a diluted liquid fertilizer to feed your plants. Feed often and lightly. btw ... make sure they have excellent drainage.
Good luck with your new roses.
