no the green house is the first place you enter, hence the ridiculously long queue lines
everything else comes after
here's how it goes from my memory:
The regular line enters the dungeon then goes out into the greenhouse
then the pass through the "oxford corridor"
then the portrait gallery
then dumbledore, dark arts, gryffindor, room of requirement
the express enters the dungeon goes into their own potrait gallery and enters dumbledores office and does the rest with the regular folk