Releases will happened in our company is based on the client
requirements .If we reached/completed all the requirements
then we go for release.dead lines reached then we will go
for the release.

My project is a product based. We already had product in 
the market launched in year 2004. We lauch our product 
(called volume) thrice a year (now decided to launch twice 
a year). We release a number of its service releases to the 
customer depending upon the customer submitted bugs + 
requests. every volume release had some new feature 
(whether internal or customer requested). we release the 
volume release in the market after verifying the product 
meets all the requirement and passes all the quality 
parameters.