It's just studio chatter.
You can clearly hear Justin say, "I don't know. Maybe I should come in this..."
Sounds more like "I don't know, maybe I should come and listen" to me. That's also more likely if in a recording studio.
More likely?
Uh, the "more likely" is what I hear. Musicians in a studio ask that question - when should I come in - more than they ask any other question in the studio. Just curious, have you ever been in a recording studio?
Ok, so what would the next words be if he said "I don't know, maybe I should come in this..." ? That line of thinking would make sense if he said "maybe I should come in at this..", as that could be followed up with the word point. "Maybe I should come in at this point", or this chord, or this drum beat or whatever. But without the addition of "at" or "on" this, it doesn't really make any sense.
However, "maybe I should come and listen" could very well mean him referring to going into the control room to listen to a bit of playback.
Anyway, I guess only Justin knows exactly what he was saying, even if he can remember !