Mis-behavior of alert calculation

As far as I have experience with alerts, when we put something like WHEN avg () OF query (A, 2h, now) IS ABOVE 5000 this means do avg calculation of the last two hours and if it was above 5000 then do alert.
This was the behavior when I was putting alert on graphs with CloudWatch. Now that I am putting alerts on graphs with MySQL source, it doesn’t matter what value I put in the second parameter (2h, 24h, 48h, whatever) the calculation does not change, and it seems to me that it is taking average of all the values in the query instead of only from 2h ago till now. Is this a known issue? Can this have something with MySQL?