This happens all the time. I found this link. Though 7 years old, the points remain valid.
Looking a the figures about 1/3 to 1/2 the shelf offerings are at 100% or more market cap. 250 million is aggressive but not ridiculously so. The dip in SP is expected because historically stocks dip after filing an S-3.
Getting the paperwork out of the way now greatly speeds up the process. They can use LPC and Cantor for the 25-30 million needed for the next 6 months. The shelf won't be used right away. My assumption, similar to a few others on the board is that the shelf will be used if there is a big increase in stock price following a successful PDD trial. Unlike some, I feel that a successful US Rett small 15 patient study will not cause enough of a rise in SP to justify using the shelf.
As far as timing, the average time to first financing was 207 days with most filings raising < 50% of the potential raise. Assuming a Q1 SP spike if positive top-line results, AVXL will be about 200 days out. Link to analysis of S-3 filings
The summary is:
Taken together, the data around S-3s in recent years, a period of economic hardship, indicate that:
Only about half of small cap therapeutics companies file shelf registrations
For those that do, the overwhelming majority utilize them, usually in about 6 months
The first drawn down is usually 50% of the shelf or less, which could give shareholders an estimate of the extent of dilution at a first raise.