Ubuntu 13.10 is set to be released on 17 October while Ubuntu 14.04 is currently scheduled to be released exactly six months later, 17 April. However, there's also some talk of releasing one week later on 24 April.
Among the Ubuntu 14.04 release schedule talk was working around Easter holidays, tax day, and trying to fit in all preferred development milestones. There was also some talk of trying to schedule the Ubuntu 14.04 LTS release around the time Microsoft Windows XP finally reaches end-of-life on 8 April, but that release date couldn't be achieved. Instead Ubuntu will try to increase marketing around that time to help push any remaining Windows XP users towards the forthcoming Ubuntu Linux release.
Those wanting to find out more about the Ubuntu 14.04 release schedule can find information from the vUDS session and then the current Wiki Ubuntu "T" release schedule.