re: What months do the Android OS updates most frequently release in?
Starting with Eclair it was 8 months until Froyo, then 7 months before GB in December 2010 then HC came out 3 months later, then 8 months until ICS, 7 months until ICS in October 2011, 9 months until JB 4.1, 4 months until JB 4.2, 8 months until JB 4.3, 4 months until KK 4.4.
So far that is an average of a little under 6.5 months per major update (which would indicate somewhere around now), however lately it seems to be alternating a long and short version of that in the form of 9, 4, 8, 4. If we assume we are on another 8 or 9, we should expect June or July (Google IO is June 25th, 26th) which would put us in line for an versioning incremental after 4 months around October (expected release of the next Nexus phone).
So far the months March, June and November have been excluded from major version incrementing updates, although June and November have both had new versions announced during their months with the actual release coming out later.
The Nexus 7 tablets have both shipped in early summer and Nexus phones for 2011, 2012 and 2013 all shipped in Q4(October through December), with the earliest being the Nexus 5 in 2013 (October 31st). The Nexus 10 released in November 2012 and was not succeeded by another version in that form factor.