Before Jack even opens the terrace door, Bruce knows he's there - he doesn't make a habit of trespassing, he's just on his way out, so of course the timing would work like this.

'Like this' meaning just as he lands silently in a crouch, balanced precariously on the roof's edge, currently neatly obscured in shadows but in very real danger of either having to immediately reveal himself or sit in a very dangerous position for as long as it takes Jack to go away.

- Of course that whole train of thought happens in a split second, and in that same split second, he decides that sounds like a terrible idea, and if he's going to get busted he wants to get busted without a leg cramp. So he just. Hops down onto the actual balcony. It's clear from how he moves that it's in the course of stalling himself from having leapt from somewhere alarming.