Was due to start my re-watch of S2 tonight anyway, so this spoiler was well timed.
If it’s during events of Broken, it’s gotta be either between leaving Gold’s, (the “punch you in the face” scene) and going back to the Sheriff’s station, (where they interrupt Regina getting her soul sucked), or between the Sheriff’s station and going to Regina’s office (to get the hat). Technically, from what we see, Emma’s never alone during those times to be chasing someone down, but I guess they could still write it in that she took a detour on her own in there somewhere. Those are the only times when it’s dark out and Emma’s dressed to match the BTS pics.