Just observationally it started with flights occurring in March, moved through that month, then went to April, moved through that month, then went to May, moved through that month (and may not be complete for the month of May).
I don't know yet if we know if these changes will sweep through June, July, etc (we just haven't had reports yet here on this thread I don't think) but to answer your question no these changes are not just for flights in the next few weeks it's for flights occurring even months in the future. So best advice you may want to watch your flights.