Really hard to answer since it depends so much on the amount of people who are following the company at that point.
The large majority of people who hear about the company only when the results are announced won't be ready to buy at opening bell. They need to do some DD after which many would probably start buying.
However, current valuation model for the AD biotechs is such that even a remote chance of getting a treatment for the disease is worth billions. SO having a clean proof of efficacy IMHO should results valuation at least between $100-$150 immediately after the results.
But if we are around $15 the day before then it most probably won't open above $100 but maybe even around $50. In this case I think there's a clear buying opportunity, which I'm planning to utilize like many others here.
Of course this requires clean results, something like non memantine group got in the previous trial or at least fairly close to that.