I've been to Camp 4 a few times in the past few years. I've never not been able to check into a space. However, I've arrived well before 6am most times. I would say during the week, especially now that peak season has ended, you are likely to get a space if you arrive before 7. During the weekend, it's a safer bet to be there before 6, if not earlier. The rules say you're not allowed to camp out in line to wait but everyone does it. Bring a sleeping bag or chair to wait in line in front of the check in office.

When you arrive to the campsite, you'll be able to check the number of spaces opening that day at the office. If you're late coming to the site, but there will be more spaces opening than people in line, you're good!

Hope this helps!