Are you testing Ammonia, Nitrite, and Nitrate? It shouldn't take long with the seeded filter -- are you using fish food or what as the ammonia source? It might be instantly cycled -- give it a couple of weeks with a daily addition of an ammonia source, and if you don't see any spikes, I'd call it cycled. Stock slowly.
You'll probably only be able to do one damsel in this size tank. You could do more, but eventually, you'll only have one. Mean little buggers. Also, some get pretty big -- Dominos, for instance. So, research before you buy!