Here's my problem with the idea.
Thirty seconds won't get you off the runway with enough E to maunerver. You'll still get whacked just off the runway.
So, after a few months of that, people will be in here wanting the time to be 60 seconds, etc.
Then maybe somebody will have the idea that it should be altitude related.
It's a slippery slope.
The solution really is to up from a different field and attack the vulchers at altitude, in force if need be. Good old fashioned fighter sweeps can be a lot of fun.
All that said, I would be somewhat more supportive of either increasing the amount of ord needed to take a VH down, or better yet, add a second VH to airfields to make it just a little harder to take the wirbels out of the picture.