Why wont Biz Jets allow somone to build their hours quickly? What if you fly for one of the larger Biz Jet companies like Netjets of Citationshares? The work seems pretty regular and I would imagine you could build your hours fairly quickly
The airlines have full schedules which are planned in advance so it is fairly straightforward to get the most efficient use of the crew resource. You only make money for the company when you are flying so they will squeeze the full 900 hours out of you. I am led to believe that even the likes of BA will fly you to the legal limit although perhaps this will be spread across the year rather than the traditional busy periods with the LCC's.
Biz Jets would love to maximise their use of you also but the nature of the owners and their requirements is such that you may end up flying around 450 hours a year with lots of hanging around and last-minute schedule changes. Not that this means you won't be as tired but it should mean much more real flying with a wide variety of destinations.
Also - don't expect to join an airline straight into a cushy route - expect to be on-call and to fly the routes that the more senior crews don't want.