Here is link to ASX statement regarding settlement dates. As I read it (page 2) normal trading (vs pre-settlement or deferred settlement trading) will not occur until 2 June. When the ADS's will trade (five S32 ordinary shares) who knows? My guess June 4 or 5, after they get the entitlements and deferred settlement basis sales figured out.
Remember, one BHP ADS (representing two BHP ordinary shares) is entitled to 0.4 S32 ADS (and each S32 ADS represents five S32 ordinary shares. Got that? So for each ten BHP ADS's you get two S32 ADS's, I think.