Two days ago, we adopted a cat. This is the second cat in our household, and both are around 1.5 years old. We did not follow the general recommendation of separating the two cats at first, instead immediately placing them both in the same room. While relations between them have improved over the two days, they actively avoid each other, hiss if they get too close and our old cat distrusts us if he can smell the new cat on us. No fighting yet thankfully. While they of course haven't been around each other long enough to get used to each other, I worry that our lazy introduction between the two cats has permanently soured their relationship. Is there a way to fix the introduction? For example, would isolating the two cats and doing the slow introduction work when they've already been seeing each other for two days.
tl/dr can two cats who have already been introduced for a short time be reintroduced in a way that makes them better trust each other?