in my experience, ive had much more luck with planting directly into soil. but some seeds may take longer to germinate depending on many factors.

ie: i planted 2 sativa, and 2 indica seeds about 3 weeks back. both sativas arose the same day about a week from planting, 1 indica a week later, and then the 2nd indica litterally broke surface at the 3 week mark. (i figured it was long gone)