Sorry, I haven't used the quinine sulfate, and I agree, those directions are a bit confusing. I would prefer any treatment for crypt to be at least 21 days, as the cyst portion of their lifecycle is often resistant to treatment.
I've purchased Chloroquine phosphate from fishchemical.com...it is a great product, although you have to purchase 1kg @ $125.
I have been treating my fish regularly at 8mg/L, or 30.3mg/gallon (hope I computed that correctly!) with great results.
Re-dose after every water change, with the correct dosage for the volume of water removed. (if you change 40 gallons, you would re-dose with 1.212g Chloroquine).