Using isinglass finings a number of times is perfectly possible but probably unnecessary. Once should be enough if time to settle is allowed. Unfortunately its use renders the beer unfit for vegetarian and vegans. That may be no great hardship (more beer for me....) but it is worth bearing in mind when offering a drink to the wider community. Also it is not necessary to use isinglass especially if one brews with "hard" water containing calcium ions. They do a surprising good job of coagulating and precipitating colloids and suspensions..
If one leaves the beer long enough to condition then IMHO no fining is needed. yeast will always drop - and even the worst case of yeast contamination will drop clear over a month. Some brewers and drinkers think a month is a long time.... but the difference in flavour and clarity from extended conditioning is noticeable.
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.