Don't bother with that formula. In H-2415 the F-5 fixer is indeed specified, but a few things need to be kept in mind:
– the documentation is based on very old material (5222 itself is the oldest emulsion still in production);
– it refers to very large processing volumes where extremely long lengths of film are immersed, sometimes over 2000 feet. In that case a hardener isn't a bad idea;
– it was designed to be as inexpensive as possible;
– the documentation specifies a full 11 minutes for archival fixing, with correspondingly extended washing times.
Simply don't bother with fixers based on sodium thiosulfate, or if you insist on using one, go for the rapid formulas. Any fixer based on ammonium thiosulfate will be better suited for your purposes.