There are no instructions for proper mixing or time so anything would be a guess. Your guess is as good as mine in this case. I guesed the same before I read your post, while thinking this over.
Ian is right that fixer used for film should not be used for paper under the best of circumstances, but it is possible to use it if the concentration is high and times are long. After all, if it became inactive, then it would immediately become useless for any more film. All it does is make the paper behave more like film in terms of concentration and time. The iodide in the fixer changes the paper emulsion into a film emulsioin (in simple terms) and that is why the change in dilution and time is necessary.
PE