Thanks for your advice, but I may have to just guess the time as I don't have the facilities to develop by inspection at home.
I exposed the ortho film without any filter, so it should look rather "normal"...probably like a panchromatic film with a green filter on.
I just got a bargain minus red filter on ebay and I'll try it as soon as it arrives to see how it works with ortho film, but, from what I've been told, I may as well have bought normal panchromatic film to test with that filter as the effect would be the same. To have a blue sensitivity only effect with the ortho film, I guess I could just cut the green wavelength with a magenta filter, but they're not very common.
These are just some experiments, I'm shooting my main project on Foma 100 developed on Microphen, so there's no risk of messing up important work I'll keep you updated with my results if you wish x