I am guessing the SN teabags have less than 3 grams of leaf in them, so I would try a little longer, 3-5 minutes. Like Nick, I also tend to brew SN at a lower temp as I like the delicate nuances this produces, usually around 165ish* in a preheated brewing vessel or cup that is around 6 ounces. If you do not preheat, go hotter, around 175-180* as the water temp will drop off immediately.
Silver Needle is a good candidate for bags since the leaves, or in this case buds, do not expand hardly at all. So, as long as the bag is big enough, you should get decent results.