A common trope in stories is dragons who shapeshift to appear human for large periods of time to disguise themselves and move among humans.
On on Earth do you manage this in Pathfinder? Unless I'm missing something, Dragons can polymorph self 3/day, and at a caster level of 16, that lets them do it for 16 minutes.
48 minutes is not long enough to pull off a long term deception.
Although the mechanics for what happens to the dragon are like polymorph, the duration is not. The dragons have the Change Shape supernatural ability, not a spell-like ability to cast polymorph (human only).
The change shape universal monster ability says "Unless otherwise stated, it can remain in an alternate form indefinitely."
Still means only tiny-large dragons can mimic small/medium humanoids, but I'd GM fiat that restriction away.