Board Thread:Questions and Answers/@comment-5924243-20130326012410/@comment-4631119-20130330175925

Well actually you can guess from the events there.

When they started, it's on Spring, and when they reach #19 at the Episode 11, its already around Fall (usual time in Japanese for School Cultural Festival). Since from what I know the Festival usually helds by Japanese schools on October, so it'll be around 6 to 7 months already.

About why other singles isn't featured, because the event required for those singles to be featured hasn't met yet, except for "Natsuiro Egao 1, 2, Jump!" which requires a beach events (but somehow skipped in the anime) and "Bokura no Life, Kimi to no Live" which requires nine members joined.

The "Snow Halation" needs a Christmas event in order to be performed, and "Mogyutto Love de Sekkin Chuu" will be performed best around Valentine's Day.