On the EGISYS website it says "Till September 5th, Poser 4 and Poser Pro Pack are available as single product and bundle at a very low price! ". So I don't think Poser 5 will be released before then. They want to sell as many Poser 4/ pro pack bundles as they can before 5 hits the shelf. If you believe the "Tuesday" clue, then it could be Tuesday the 10th. Or as it's Poser "5", it could well be the "5" th itself!

Daz Studio 4.8 and 4.9beta, Blender 2.78, Sketchup, Poser Pro 2014 Game Dev SR5 on Windows 8 Pro x64. Poser Display Units are inches