OM-D EM-5 - sensor cleaning and Art filters?
Is there any control over the timing, or is it automatic at power-on, or by pressing a button etc.?
No, it automatically happens when turning on.
As for wet cleans, if some condensation dries or pollen sticks, then Olympus says to have them do it, as there is some talk of warranty killing if the user does it, plus more talk of some anti-static coating that needs to be re-applied after a wet clean. No idea what the truth is.
As diffraction starts to diminish resolution at f/8 and beyond with M4/3 sized sensors, then because of the distance from the front supersonic layer to the sensor, the occasional dust that does stick never really shows. Use f/22 and then find dust that never appears at "normal" apertures.
All I can say is that with 4 different 4/3 and M4/3 bodies in over 8 years of use, I have never had a dust problem.