Except these were NOT hostages, ...they were arrested for being in Iranian territory without permission.
For all intents & purposes, they were illegal immigrants if ya wanna get technical.
They were NOT hostages. They were under arrest for suspected espionage.
Furthermore, I doubt they were incarcerated long enough for Stockholm Syndrome to come into play.
The status of the captives isn't the issue.
The Stockholm syndrome describes the phenomenon of when a captive becomes increasingly loyal with his/her captivator.
Whether the person is a soldier from a foreign country held imprisoned, or otherwise, there is always a risk of this Syndrome to occur.
And no. The Stockholm Syndrome doesn't need longer time to develop.
It develops very fast, originally it was coined for a situation in a famous bank robbery gone wrong in Sweden in the 70's, with a hostage situation. I think the drama lasted for 2-3 days or something, at the most.
-Hedge