They do not take ADRs. You just go and if they are filled up, they take your name and give you a beeper thing (you can't go far away though). If you go in the middle of the afternoon - like 2:30-3:30, it probably won't be so bad, but in the summer it's more crowded than winter. We were there in January around 3 PM and we were almost the only ones in there.
Or go when they first open, but I'm not sure what time that is.