Yes, add the meds, but when you add you will have to stall on the hypo.
Here’s the way I see it. You need to get moving on the antibiotic because the symptoms seem to indicate bacterial infection. I am suggesting hypo not so much for ich, but to reduce stress. However, at this point hypo is secondary to the bacterial problem that seems to be going on.
Thus, to gain the full effect of the antibiotic you can not dilute the treatment water by trying to achieve hypo. Dose and then the next day, 2-3 hrs prior to redosing, you can perform some more water changes to move toward the hyposaline conditions of the water. At the same time, if you have carbon filtration, use it to clean up your tank [since it is uncycled]. Do this during a 2-3 hour window. When done, then redose with the antibiotic.
Keep the lights off in the QT [if you have aquarium lights, but don’t keep the sick fish in complete darkness during “waking hours”]. Room lights are good. Antibiotic potency is diminished by UV from lights. However, when you begin the hypo process, you can turn on the lights. This would be a good time to try and offer the fish food as well as for you view the fish’s progress. Again, lights on only towards the end of the 24-hr dose [when you are going to do maintenance/hypo on the tank.
Anyway, that is what I would do, and do do with sick fish that need to be hypoed but also need antibiotics.