Did they have ich before? Or is this prophylactic treatment?
Theoretically from what those above said, 30 days treatment will mean no ich on the fish. And probably no cysts but who knows you could have one of those bad strains.
Moving them immediately to DT means you don’t have to worry about those freak cysts re-infecting your fish. But the risk you take is that if the copper treatment wasn’t successful (e.g it dipped below 0.3) then your fish could have suppressed ich. So I guess it depends on how confident you are that your treatment was successful. If not then I would consider leaving them in the QT and observing. Better they get ich and you re-treat them then infecting the DT.
At least this is what I believe Humblefish means.
I have a Naso and PB in QT. So far no signs of illness, but I’m terrified to not treat with the one fish that would be considered the “ich magnet”. I know there is debate on this. But if they have been fluke/other illness clear (3 weeks so far). I could absolutely treat for 14 days and out into DT directly. If they were showing signs of illness I would be much more hesitant.