Ubuntu 10.04 Lucid Lynx stable version is schedule to release in April 2010 and if you are interested in knowing the schedule time for other versions of Ubuntu then here is a compiled video with release schedule till Ubuntu 11.04.
This video has also detailed the LTS (Long Term Support) time range for Ubuntu 8.04 LTS and Ubuntu 10.04 LTS. It also provide some information about the origin of different names of Ubuntu i.e. Karmic Koala, Lucid Lynx etc. Did you know the release date of Ubuntu 4.10? You can get the answer of this type of question in this 1.44 minute video.
Ubuntu Release Schedule Video