I find multiple sources having both dates for this match: either 2004-06-30, or 2004-07-01. Wikipedia is no help in multiple articles, as single matches aren't broken down to dates.
I fear that from USA's perspective it was June 30th, while on location (London) it was already July 1st. But since agencies and article writers are still not paying interest in stating timezones I'm lost on this. Inspecting pictures is no help either, as sometimes "date created" means "date modified" due to improper metadata usage.
Maybe the match was paused by raining and continued the other day, but I haven't read that anywhere.
Additionally I'd also like to know the on-location dates of Sharapova's other matches during Wimbledon 2004, but that's more a bonus.