When you apply for a Whitney permit, you specify “Day Use” or “Overnight”. Both permits allow you to enter the Whitney Zone on a specific date. You can enter at any time on that date.
The Day Use permit is intended for people who don’t camp or otherwise “spend the night” in the Whitney Zone. You should be out by midnight, but nobody is going to write you a ticket for staggering out a few hours late if your trip took longer than planned.
As the name suggests, an Overnight permit is intended for people who spend at least one complete night in the wilderness (Whitney Zone or otherwise). In other words, it’s intended for people who are camping. You can spend multiple nights, and you don’t have to spend the exact number of nights you specified on your application.
Rangers tend to be reasonable people, and they won’t write you a ticket for aborting your legitimate Overnight trip because of illness, injury, major equipment failure, or other emergency. On the other hand, if you have an Overnight permit, and you leave your tent and sleeping bag in the car, and you enter the Whitney Zone planning to do a dayhike, you are abusing the system. Please don’t do that.
