Board Thread:Questions and Answers/@comment-223.182.8.114-20180405101538/@comment-25669516-20180406073405

The first four bosses (up to Widow) were added at a gap of one month each. After that, for Shogun, there was a gap of three months. Titan was added more than an year after that xD

See: List of Updates (SF2)

Due to the size and scope of SF3, it takes longer for updates to release. There was a gap of 3 months between chapter 3 and 4. If chapter 5 follows similar non-linear storyline, it may require a longer time as well. We'll probably get some events as well in between.