Those ramps are in the State Parks. It is because the state park does not open till 6am. Just use a different ramp on the lake. Pretty much all state parks have hours and closed to access at night. If it is one of the parks that has a way for paid campers to come and go after hours, I have paid for a basic tent camping spot before as a way to enter a park to launch before they opened the next morning.
"Onward up many a frightening creek, though your arms may get sore and your sneakers may leak. Oh! The places you'll go!" ~ Dr. Seuss