so I've never used dry ice before. I found a place in my town that supplies dry ice pellets by the kg. my questions for you guys are 1. How long does it last. The party I'm hosting doesn't start until 6:30 pm on a Saturday and the store that holds it closes at 11:30am! Will it not last that long? 2. How much of it will I need if it does last. I just don't want it all to be a bust. All answers welcome!