New, healthy anemones should attach within hours. If an anemone is not firmly suctioned onto the rock, I repeat, do not turn on powerheads. I think you may be confusing attachment with permanence. Just because an anemone is attached doesn't mean that it can't or won't move. You just don't want a free-floating anemone with powerheads on. Trust me.The only issue I see is new Anemone's wont attach right away, they can days to find a good spot. They need the water movement to find where they will be comfortable and happy with not only lighting but water movement.
I would run the pumps all the time.
Also what are your water conditions? How old is the tank? Is the lighting new/old? How did you acclimate it and for how long?
Anemones are very sensitive to any change in water chemistry. It can take a few days for a specimen to perk up unti it adjusts. How was the coloration? Was it dull and not very colorful? if so it could have been a new shipment and was still stressed, or wasnt healthy.