If you are free to go, then it is legal to not pay you for that time. A worker must be paid for all time spent working, which includes time spent waiting at the work site without work to do, if the employee is required to stay there. But if the employee is told that he or she is free to go but to back later, then for the time they are free, employees don't need  to be paid. The fact that the plant you work at is isolated, instead of being in an urban area with more choices of what to do, does not change this rule.