Well std. requirements are first of all the right to fly Danish registred aircraft - which means a danish or a JAA license, preferably with endorsements for the Citation (2 I think) BE200 and BE1900. While chaps with this profile are somewhat rare, less will probably do it, but everything boils down to the old supply & demand thing.
Std. contracts are for 3-6 months on and then off untill they need you again basically. Some flexibility is expected though. Generally it is a good outfit. Treat them well, and they will treat you well....