3 starter questions

Just a few questions, any help would be great.
For some background, I start on Monday.
1)When is this thing about union taking money out of my paychecks? How long do they do it?
2)How long is the probation period? And what exactly does it mean?
3)I work from approximatively 5:30-9:30, I've read that you just work until you fill/unfill your trucks. So if I'm a fast worker (once I get it down, I'm confident I will be) and finish in say 3 hours, do I only get payed for 3 hours? If so, should I work slower?

Thanks for any help with any of the above questions, especially number 3!

This is for UPS by the way.

1. they start after 30 days, it lasts 3 months, 20 dollars a week and then 20 dollars out of the first pay check of each month
2. probation period is 30 days, basically they see if your up to snuff to do the job, afterwards you begin paying your initation fee and your in the union, and its next to impossible to get rid of you
3. this is where it gets kinda tricky, they get rid of you as soon as they dont need you to do your job anymore, which for a new hire is roughly 3 hours or so into the shift, but can be as long as 5 hours for a guy with more seniority. #1 trust me you wont be a fast worker, this job is hell getting acclimated to, #2 if you go to slow they'll just cut you earlier and have someone else wrap up your trucks and cut you earlier, but you get paid down to the minute that you work. UPS makes no secret that this is a difficult physical job, however until you get on the belt you have no idea what your in for, most guys loose anywhere from 20 to 60 pounds within the first 3 months from when they start, for me it was 50