I have been thinking, Russian's love to make a point, Putin in particular. So why give Snowden asylum on 1 August? What because it was Wattle Day, horses birthday, they like Thursdays?
Well it might be this reason:
On 1 August 1914, Russia entered the Great War (WWI) by declaring war on Germany.99 year anniversary of the start of the Great War, sounds like a fitting day for Putin to show the US the finger.