Well, Its certaintly not impossible to Hit all Adult Coasters in 1 Day, because I managed it in my trip with re-rides(and it was my first ever Trip there) after excucuting a perfect Plan of avolding queues, It worked an absolute Treat.
Like Jeff Says, Its not impossible, Queues were quite short on the day(s) I went, So even I could have managed it If I wanted too, I had all coasters under my belt by about 4-5PM, so that would have left me a good couple of hrs to fit the rest of the Adult Rides in(all Flat Rides were Walk Ons basiclly) But I was mainly riding RollerCoaster after RollerCoaster, so rarly rode any Flat Ride, but I could have done it, It's certaintly not impossible by any means