I had the bike shop put mine on my upright in early October. It was a little early, so rode my faster hybrid with slicks until November. We got a good dump of snow and freezing rain on Halloween.. but usually by November the overnights are cold enough that the pathways ice up if there is any humidity so I like to have them on by then. Now we are solidly into winter. This year studs are only going on the 26" upright, the hybrid with 700cc tires is not going to see winter this year (although it has 3 under its belt).
and no I wasn't going to do it myself... with no quick release a IGH, fully enclosed chain, dynamo lighting and fenders I'm not up for changing this bikes tires yet - its a PITA, totally worth supporting our LBS instead :)