DW and I check-in for a long weekend soon and will be at the Fort by 7:15/7:30AM as usual. If things go as usual we will be at our site 15 minutes after DW goes into the Outpost for paperwork and if not then it is to the Overflow Lot we go to park and start our stay.
Check-in time is 1pm but I have never checked-in that late. Just like John said above we check-in early in the morning and most times we get our site assignment right away. You don't need to pay attention to the 1pm time, it doesn't really apply at the Fort. If your site is ready-you get it.