Whirfloc: .5 of a tablet in the last 15 minutes for a 5 gallon batch. Anymore and you are using more than you need to. This is one of those ingredients where adding more is too much and could possibly be detrimental to your batch. For proof of this listen to the 1st Shakespeare Stout CYBI where JP used too much Whirlfloc and had to scrap gelatinized wort pancakes off the floor at the end of his brew day.
Ha ha ha, I totally did this with Irish Moss my first time. I poured the whole packet into the kettle, instead of measuring out 1/2 tsp. By the time the 4 gallons was cooled down to pitching temp it was a thick slimy mass of worty, syrup-like sludge...that I poured straight into my fermenter and drank 6 weeks later.