Agree with larryi above speed once set should stay unless your ac fluctuates during different times of day especially if everyone is using lots of electricity given the heat wave most of the country is currently in.
High electric use can result in lower voltage, but that wouldn't matter in this instance. The Basis uses an AC synchronous motor, so its speed is dependent on the line frequency. That's something where utilities have to maintain to a pretty tight spec, because the stability of the grid requires it.