Flymeboy, as answered in your other thread, its a), descend NOW. If it was at your descretion, you would have been told 'descend when ready FL200'. The level restriction is given as it has to be, and then fully complied with for noise abaitment (big bang) procedures. It doesn't mean level off exactly 45nm b4 BNN (although thats fine), but you must be level by 45nm b4 BNN.