point of interest: in me3mp only balance changes we're weekly and they didn't stay weekly for very long, it was later changed to bi-weekly and then monthly and then nothing
don't expect too much, BW is now aware of how much work weekly changes are and will likely not do them that often
ME3 was release on March 6 2012.
Balance changes were weekly for almost a year (50 weeks, Christmas excluded) then it simply stopped. There were no monthly or bi-weekly balance changes, unless you count the final changes that skipped 1 week, but this happened only once...
As for Weekend Challenges, they started on March 16 (10 days after launch). They went on a bi-weekly basis until October 19 2012, then went on a weekly basis from October 26 2012 to March 5 2013. Operations ended on March 5 2013, 1 day before a full year from release.