The new iPad goes on sale already on Friday morning. This means queues start latest at midnight.
The first wave of the new iPad is sold out online and you have to wait 2-3 weeks if you order now. The next best chance to get a new iPad on launch day is to score one at an Apple retail store. 9to5Mac received an image that reveals that Apple will start selling the new iPad already at 8am on Friday.
I expect that queues will be forming around midnight if not earlier in front of Apple Stores. Update: First people are already in line at an Apple Stores. The quantities of available new iPads will be likely very limited.