Hi [...],
2mg hypnodorm (rohypnal) is roughly equivalent to 20mg valium.
Anyway, as far as tapering, hypnodorm has the same half life as valium. As [...] said, it's best to taper off one drug at a time. Much simpler. No need to deal with a cross over. You may want to reduce the hypnodorm first as the smaller mg pills make it more potent and may be better dealt with first. It's up to you though, of course.
For the hpynodorm, what mg pills do you have? If it's 1mg, (I think that's all they come as?) you can reduce by a quarter pill every week or two. If this becomes too difficult at the lower doses, we can always help you with a liquid titration. This entails mixing your pill with a liquid and reducing small daily amounts.
As for 20mg valium, you can reduce by 1 to 2mg every week or two. As you get lower, the cuts can be reduced. It's best if you have 2mg valium pills for your taper, at least as you get lower.
Remember, all of this can be adjusted(size of cuts, speed of your taper) as you go, depending on how you are feeling.
Take care, welcome to the forum.