Ive never done it but plan to a few times this coming year. I believe late june/july is when the snow is melted enough. But that all depends on this winter and by the looks of it pretty dry so far:sure:
Labor Day weekend is usually good. You need to prepare for cold weather in case of a storm. Check the Rubicon forum on Pirate for other groups or events that might be planned that weekend as well as trail conditions and weather updates.
labor day weekend is fine. Plan for snow and bad weather and if it doesn't happen you are over prepared and thats fine. Pay attention to pirate and other sites where folks will be posting up more frequent updates on the trail.
April I say no chance, we've run it the last 2 Memorial Day weekends. The trail has been clear but it has been cold, snowed on us 2 years ago. Washing up at buck island was painfully cold and swimming is out. I've found it's more fun later in the summer when the water has warmed a bit.