9to5 Mac is reporting that Apple retail stores both in the US and abroad are planning an overnight workday on Tuesday, July 24th.  These overnights usually proceed major product launches, and allow the staff to put up signage and do last minute training on the new products.

“We’ve heard a few whispers (three and counting) that Apple Stores both in the United States and overseas have planned overnights for Tuesday, July 24th,” the report notes. “With OS X Mountain Lion launching ‘in July,’ according to Apple, we believe that it is sensible to speculate that this overnight may point to a public launch the following day.”

Mac|Life has another clue:

There could be one clue in last year’s release of OS X Lion: The release was announced during the company’s Q3 2011 earnings call on July 19, with availability the next day in the Mac App Store. Apple has a quarterly earnings call next Tuesday, July 24, so… we’re just sayin’…

The next version of Apple’s desktop operating system, OSX Mountain Lion 10.8, will only be available as a download in the Mac App Store and will cost a paltry $19.99, and can be installed on every Mac you own for the one time cost.

New features coming with the big cat include many more iOS-ifications of the operating system, bringing desktop versions of apps like Notification Center and Reminders.