The hostage rescue is available on attack & defend on the levels Border Town and Library. You must be on the attacking team. The main goal of hostage rescue is to escort the hostages to the designated space on the map. The hostages are generally located in the center of the map and can be escorted by walking up to them and telling them to follow by pressing A.
The fastest way I have found to get this achievement is to head to the Library and then get both hostages to follow and then head to the drop off point.. Hopefully you won’t run into much opposition since you need to get the hostages on your first try in order to make it in time. You can also get a friend to sit on the other team and do nothing.