RE

... i'm wondering if i could just double the
fixing time and use the 1+9 instead of the 1+4 (as the 'strength'
of the 1+9 should be half that of the 1+4). would that work?


If that were the case a 1:24 dilution, 1/5 film strength, would
take 40 minutes; allowing for 8 minutes at 1:4. Such is not the
case. I expect 8 to 10 minutes at 1:24. Exceptional films might
take a little less or more. Conditions: 20ml of fresh A. Thio.
concentrate in a solution volume of 500ml; agitation 1st
minute continuous and 15 seconds each there after.
One-shot use. Dan