To enter the hunting grounds at the Warzones 4, 5 and 6 you'll need to break one of the machines located on a room accessible right next to the hunt entrance, after that you'll be able to pass the teleport. Once you enter the hunt, you can exit and re-enter freely for 8 hours. After that, you will need more points to break the machine and enter again (you will not be kicked once the 8 hours are over, so you can stay how long you want as long as you have entered before your time is up)
However, the number of points required depends on if you have the Bigfoot's Burden quest complete or not (Warzones 1, 2 and 3). If you do, you'll need 10 points and if you do not, it'll be 15.
You can make some tasks to get some points so you won't have to buy as many Suspicious Devices. For more info, look the spoiler for the Dangerous Depths Quest.
Good luck and happy hunting!