In the work of WH Smith, bookazines have a shelf life of 12 weeks. My top publication is reaching the end of this and so they are clearing the remaining copies by knocking a couple of quid off the cover price. According to the shelf flash, you've got until Wednesday to grab your copy, or your extra copy if you sensibly bought one the moment it came out.
Don't worry if you can't get to Smith's, it will still be available on-line.