When introducing cats.. should I wait until they stop hissing under the door before letting them see each other through a baby gate?

We’re following Jackson Galaxy’s method of introduction and haven’t let the cats see each other yet (it’s been 3 days) but it wasn’t clear to me when to move to the next step. They’ve gotten a lot better but currently my original cat still occasionally hisses/growls under the door at the new cat. Should I wait until he stops hissing altogether before introducing them through a baby gate or will the hissing never stop? 😅 They both come from hoarding situations with lots of other cats but my original cat hasn’t had cat contact in 2 years so he’s acting a bit confused/territorial.

We’re following Jackson Galaxy’s method of introduction and haven’t let the cats see each other yet (it’s been 3 days) but it wasn’t clear to me when to move to the next step. They’ve gotten a lot better but currently my original cat still occasionally hisses/growls under the door at the new cat. Should I wait until he stops hissing altogether before introducing them through a baby gate or will the hissing never stop? 😅 They both come from hoarding situations with lots of other cats but my original cat hasn’t had cat contact in 2 years so he’s acting a bit confused/territorial.