This is a common idiom in English, e.g.:- "if & when the doctor comes, I hope she'll do something to relieve my pain" The idiom is using using two variables, the second being dependent on the first. The time I decide to do something depends on whether or not I'm actually going to do it at all. In the above example the idiom means 'the time that the doctor comes depends on whether she comes at all. "If and when I go to the shops, I'll get your magazine." (There's no certainty I will go, but if I do, that's when I'll get the magazine)."