sorry ... typing error.
I meant 9min 30sec.
OK thanks but I still I don't know why 9 mins 30 secs is harmful Do you mean more than 9 mins 30 secs will give you over exposed negatives with Ilford Ortho +? It might but neither of us know this to be the case. It won't be harmful in the sense of ruining your negatives.
Unfortunately no-one seems to have used FX 55 with Ilford Ortho so 9-10 mins is based on my reasons that FX55 is close to Microphen as it has the ability to increase film speed by up to 2/3rds of a stop based on John Finch's test on FP4. Microphen has a similar ability
As I said if I were you then I'd either try to establish my own speed and development time as John Finch does or at least cut a film into 3 parts and develop one part at say 8 mins then examine the negatives and decide on the time for the next part, say 10% more and do the same for part 3 if the second development time is still not right.
pentaxuser