The difference in opinion here comes from both the change in paper (fiber predominant when I started in 1964) and the modification with written material on the subject (back then, 10 minutes was not considered excessive).
When Ilford came out and said that 45 seconds was adequate for their Multigrade RC, I gasped with joy. Actually, I have done tests (only ONE fixer, not two in succession). Paper, if it is dry (neither developed nor fixed) will start to turn brown after about five minutes in strong room light. Well, I tried fixing multiple tiny pieces of Multigrade RC paper for: 10 seconds, 20 seconds, 30 seconds, 45 seconds, 60 seconds, etc. Rinsed, then I left each piece of paper in strong light. Starting with the ones fixed for 30 seconds there was no change in the white base. Assuming incorporation of a conservative 'safety factor', the 45 second minimum offered by Ilford seems good. When I tried this test with old Kodabromide paper (fiber) the necessary fix times were at least twice as long.
Papers changed through the years, as did the determination by the manufacturers for how long to fix. Ten minutes, even five minutes, were probably ALWAYS too long, but, perhaps, the long times were promulgated for reasons of conservatism and maybe even to mitigate the perception that many workers were sloppy and did not change fix baths as frequently as they should have. Long fix times also carry a possible, tiny advantage, as they just start to erode (almost imperceptibly) the threshold density. That threshold density can include a very tiny bit of base fog which removal thereof can actually improve the print quality. When I was fourteen, I left a slightly overexposed print in the fixer when my mother called me for lunch. (I did not know what I was doing or that I should not have been doing that.) After lunch, I came back to the darkroom and was stunned to see the most beautiful tones I had ever witnessed in that 'overfixed' print. Point made.
Of course, 'two baths' is more secure, and allows more leeway, especially with regard to a bit of sloppiness. But that security is unnecessary if you follow recommendations exactingly, as per manufacturer. - David Lyga