Thank you both for your answers !
It looks that - as malaguti points out - I probably should have had a look in the book before asking the question. Weinstein doesn't explicitely states it, but the way he describes the process makes it quite clear that the time reference is when the low actually happens, and not the moment in which I rise the stoploss. Looking at its graphics confirms this, though they are not easely readable.
Isatrader, thanks for your graphic illustration. Very clear. I notice that my screenshot wasn't that clear as it could have been. I should better integrate the idea of initially protective/later agressive stop, because I always tend to tighten my stops to much in the first moves, because of fear of losses.
