Is your hope that more people will be drawn to Universal and therefore the crowds at WDW may be less? If that is your goal, then timing for the grand opening hype may be a good idea. If your goal is to do both US/HP and WDW, then I'd go for later in the year after the true opening hype has had a chance to die down a bit. Although for the first year I imagine the draw at US will be increased (vs. prior US attendance..not higher than WDW).