We went at the end of April last year and the crowds were very good. It was the Flower and Garden Festival and some dates were Grad Nights but it never made it worse. I think it is a good time to go.
I agree - we have been at this time of the year a couple of times.
Providing you miss Easter the crowds will be fairly low , plus the weather is perfect too.
We went mid May this year and found the crowd levels fine, busy but not too busy. Weather the week before we left was showing mid 80s but by the time we were there it was into the 90s although slightly cooler in the evenings.
We had one day of rain and it did end up being quite cold that day and so we went back to the hotel in the afternoon but by evening time it had cleared up and was warm again