We went in April and crowd levels every day were 8s and 9s. As long as you have a good plan, you can manage. We got to the parks early and got a lot done before the crowds arrived. During the night parade one evening, DH & DD got on BTMRR repeatedly.
Another DISer once told me that she prefers nights because of the cooler temps, etc, and that she was able to get a lot done because crowds are thinner near closing time. I prefer to keep my kids on a schedule, though, so we get up early. So, whatever you decide- early or late- just research that strategy and go with the flow. When it started getting crowded, we left to swim in the pool.