Portugal
If you are invited to an interview, after mentioning that you can't start until July, then they would need to honour that if they offered you the job. If they don't have courses in July, you would probably find yourself in a holding pool.
The 900 hour rule is an interesting question. They way WW is set up, there is no real way to single out someone and work them hard so they run out of hours. The operating contract is the same for temporary and permanent crew. The 900 hour limit is more of a problem at LGW because they have less time off between flights AND they operate both long and short haul.
I've read on forums that they plan to work temps up to 900 hours so they won't be re-employable at the end of their contracts but I really can't see how they can do that in 10 months (factoring 1 month of leave). It is more about putting some slack in the operation so people on transfer lists can be moved around.