Id tell them right away, so they will get use to the fact that you are moveing out of state.
if your parents are clingy they may ob<x>ject but it would be mean to just up and leave, they may try to apply excess pressure to cause a new break in your relationship. tell them 2 days before you leave over a nice dinner in a crowded restaurant.
Negative people are everywhere but you should tell them soon
tell now. if you wait that will look bad on both of you and will make them hate him even more. just make sure you explain to them the reasoning.
If they are the negative people, I'd tell them later than sooner, but if you and they are on good terms, I'd let them know as soon as possible.
Best to allow them time let the situation sink in.