Microsoft might release the Windows 8.1 Update 2 on Aug 12. The update was always expected in August, though no specific dates were mentioned, so far.
Microsoft, too, hasn't confirmed the rumoured Aug 12 launch date even though it seems probable on at least one count. It's a Tuesday and Microsoft rolls out its bug fixes and patches on the second Tuesday of every month, something that is referred to as the Patch Tuesday, as is mentioned in Ubergizmo.
There is another reason though for users to pin their hopes on the reported Aug 12 launch date for the update. The rumour has its origins in the Russian site PCPortal.org.ru which has a reputation of sorts in being fairly accurate with its predictions.