The only time I shut my skimmer off is for cleaning, and I have a skimmer rated for a 300 G tank on a 50G tank, my 15G nano has a skimmer rated for 250 gallons.
I don't think you can overskim, I also don't think the biggest skimmer in the world could ever get your water as clean as it is in the ocean.
JMHO,
Whiskey