How long does it take for Zebra finches to wean?

I have 2 adult Zebra finches who have 2 babies. The babies just left the nest today for the first time. One 9the first to hatch) has full feathers and can fly pretty well, but the other one still has some fluff and can't fly. I had to put him back in to the nest. The parents are still feeding them a little, not as much though. How long until they can eat on their own? How soon can I remove them?