Well, I guess it all depends on when you go. The toll booth people leave after 6 pm.. we got there after 6 and no one was there to take our money!
So we drove on through.. we stopped for a few seconds to see if they were walking around the booth or getting something under the chair..
If you stay the entire day at DC, until close, and leisurely leave and close the place out (like we did) and take tons of pictures... you could get there at 6 pm.
But if you want to go to Seaworld at park opening you will have to pay, we did once.. the rest of the time we did Universal during the day, and then hit Seaworld at night after 6 pm.