That's an insinglass product (fish gelitan). You can add it multiple times with no adverse effects. Usually a proper dose just once combined with cold crash will make a brilliantly clear beer. Each pack is a dose for 5 gallons of beer.
All finings need time to work most work by collecting particles and dropping them via gravity. Cold crash helps this along, while I've seen them clear in just 24 hours I usually give them a couple days, even then there is still sludge in the last pint of a keg. So longer you can let it crash the better (2-3 days) and rack carefully, don't get greedy I've never regretted leaving 1/2 inch of beer above the trub.