Friday, July 3, was a national holiday, meaning that this was the day Independence Day was celebrated, since July 4 was a Saturday. Banks and all government offices were closed. There was no US Postal Service delivery. That is what is meant by “a national holiday” in this context.
I know, dear. I was being snarky.
In that context, it would have been more accurate to say “on the eve of the national holiday”.
The careless shuffling of holidays to suit the govt. schedules is a peeve of mine. The author was just reinforcing that foolishness by stating that our July 4th was actually July 3rd!