There is so much misinformation and lack of information about fixing, even here on APUG, that a dedicated, sticky "Proper fixing and testing techniques" thread might be a really great idea.
A couple of observations.
The Ilford "stronger fix for shorter times" strategy is predicated on the idea that a stronger ammonium thiosulfate fix will do the fixing job in the emulsion before it has a chance to soak deeply into the fiber-base of the paper. The idea was to reduce the washing times, use less water, etc. This system works, but the fixing times have to be really short and the fix has to be fresh, fresh, fresh. It uses less water for washing, but in practice often requires more fixer... unless you're using two-bath fixation over several cycles.
And, if you end up fixing for more than two minutes, you've saturated the paper base with fixer and have to use longer wash times anyway.
None of that means that longer fixing times make anything "unwashable." One just needs to use a wash aid and extend the wash time enough.
And, this doesn't mean that the regimes recommended by Kodak and others (with longer fixing and washing times) are less effective.
There are lots of papers and fixers and workflows. The only reliable way to see if your processing is getting your prints fixed and washed enough is to test the prints themselves for residual silver and hypo. The tests are easy. I really don't see why more people don't do them. I test the last print of a batch every time I print. A drop of ST-1 and a drop of HT-2, wait three minutes and, voilá, I know if my fix and wash have been adequate. I haven't had to re-fix or re-wash a batch for years now, because I know where the limits of my regime are and I give them a healthy safety margin. I still test.
My prints don't ever have yellowing problems... even after being displayed on a wall in direct morning sun for 22 years...
Fixing is likely the most complex part of photo processing and there is a learning curve to getting a handle on it. I don't understand the exact chemical processes completely, nor do I have a complete grasp of all the subtleties of designing and testing new fixers like PE does. That said, I've read enough over the years to have developed a certain confidence that I can intelligently use fixers of all kinds, do the processing and testing, and produce prints with optimum permanence. It's well worth embarking on the journey and reading about fixation in detail enough to do that for any careful worker. Many here obviously don't even follow the directions that come packaged with the fixer they are using... and end up with underfixed and underwashed prints that end up yellowing... then they post here and complain... Oh well.
Best,
Doremus