You can bid once you've completed your final line check. Bid's are due before the 13th of every month. If you complete your line check on the 15th, you at the mercy of the rostering Gods for the next month.
As for bidding awards. Rosters are not awarded based on seniority (I'm not really sure how they are awarded), so you stand a decent chance of getting North American destinations if that's what you bid for.
The duration of time until you're released onto the line can vary based on when you join, some go through in 4 months from date of hire and others it will be 7-9 months. Just depends on how backed up the training dept is (right now from what I gather it is pretty backlogged at the moment).
Welcome to the desert?