"Second question, how do you changed the clocks display? I've seen it counting up sometimes, counting down sometimes... Is there are button to control that?"
You don't. Team 1 has 20 minutes (default) to beat the map in. Team 2 must beat team 1's time, so it'll count down from whatever time it took team 1 to complete (or 20 minutes if they didn't complete).
The winner of siege is the team with the lowest completion time.
I'll post some jedi tips for Hoth later maybe