“But once Rausch was definitively gone for the day, the office transformed itself as instantaneously as a pumpkin into a carriage. Music was turned on (they rotated among the fifteen of them who got to choose), and takeout menus materialized, and on everyone’s computers, work for Ratstar Architects was sucked back into digital folders, put to sleep, unloved and forgotten, for the night. They allowed themselves an hour of waste.
How to understand "pumpkin into a carriage" ?
I understand it, say that, after confirmed that the boss had leaved, the staff immediate highing.