The timing of Neptune Insurance Holdings' IPO couldn't be more opportune.Neptune, the nation's largest private flood insurance, debuts on the New York Stock Exchange Wednesday under the ticker symbol "NP." The company sold more than 18 millions shares in its initial public offering at $20 apiece.The company's first trade comes just as the U.S. government has shut down, meaning the National Flood Insurance Program (NFIP) isn't accepting applications or processing new claims."Neptune is open for business," sa ...