I leave it in primary for anywhere from 2 weeks to 5 weeks. The minimum time is not up to me, it's up to my little yeast buddies. Sometimes my pipeline is so full that I'm not ready to move it yet, so I'll leave it for a bit.
I dry hop in a 5 gallon paint strainer bag, so I dry hop in primary.
I add the gelatin at cold crash and typically cold crash for 24-48 hrs, depending on the availability of a refrigerator. Make sure you rehydrate the gelatin with room temp water for about 20 min, then I add a cup or so of very hot water to bring the mixture up to about 160. This dissolves the gelatin into liquid form.