Listening to those moments right after he exits the balcony, I am pretty sure he did not lock the door right away. I can hear it shut, and around the time Warriena starts faintly screaming, I hear a sound very much like a lock turning. More screams, the neighbour screams too, I think, .. silence.. and THAT is when he starts hyperventilating.
The 'unscrewing ' sounds happen about 4 mins later and are distinctly metallic. It's a rapid sound, like it's being undone quickly, not done up. Not a small item, something with substance. At the ends of that, a couple 'clanks' like something coming apart. Then faint sirens.. then what I suppose is the front door, and then the elevator bings.
Re "Manchester" - Tostee says this, trying to make sense of what W is saying.. in her NZ accent, "Winchester" sounds like "Wunchester".