Hello Sonu, welcome to Cruise-Chat. Labadee is RCCL's private beach area and no visa is required.
The cruise line are getting very serious about bringing alcohol on board. I personally don't think it's worth taking a chance of being caught.
It's about a 20 minute taxi ride to the Port of Miami from the Miami airport. The price is about $25. Even with heavy traffic you should be at the port around noon.
Can't really help you with the time ticker. My wife and I are sailing on the Navigator the same day you'll be on the Voyager. I have pictures of the Voyager cruise we took in December, if you would like to look at them CLICK HERE