It's pretty clear that the story doesn't take place any more recently than the first decade or so of the twentieth century. The Zuiderzee was enclosed and drained beginning in the 1920's, and was renamed Ijselmere. The windmills and the candle point to a time prior to electrification, and the clogs and snow (Amsterdam doesn't freeze over any more) indicate a historical setting. The tugboats put us no earlier than the mid-nineteenth century.