I think you will find that the instructions say to dilute your rapid fix 1:7 for paper and 1:3 for film. Typically, you are instructed to fix the paper for longer times. However, some 20 years ago, Ilford developed a method in which one uses rapid fix at film strength for only 60 seconds to fix paper. This prevents the paper from absorbing large quantities of the fix and allows for shorter wash times. This is the method preferred by most photographers today.(posted 9005 days ago)However, there should be no problem with keeping diluted fixer until you have used it up, whatever dilution you may use.