Does a hero suffer wounds from new minions as Darkness Spreads?
This question has been asked before. Luckily, the designer has clarified the answer. You suffer wounds at the end of your heroic actions when minions are in your location, not during the Night when new minions are placed.

Wounds are suffered at the end of your actions - the end of the Daytime Phase of play and prior to drawing Darkness Spreads cards. If Minions appear on your location by a Darkness Spreads card, you do not suffer wounds to them.

You will also note that the rules regarding wounds suffered in this manner are covered within the Daytime section of the rule book, and not near the end of the rule book covering Night.