Kepler is designed to find the first Earth-size planet candidates orbiting stars in the 'Goldilocks', or 'habitable' zone. This is the region around a star where the temperature is not too hot, not too cold, but just right. This zone is far from a hot, blue star, so any habitable planet around a hot star would have a long-period orbit. For cooler, redder stars, a planet in the zone would be close-in and would orbit in several weeks or months.
Image Credit: NASA