The short answer here would be no. Places campaigns are only triggered when a user enters or exits the geofence. If a user is already inside the geofence when a new Places campaign is created, they won't receive the message until they exit or re-enter the geofence (depending on if the campaign is triggered on exit or entrance).
To get a better background on Places & geofences read up on it here as well as more information on Messaging with Places.