Not necessarily. An incubator is not needed if the dip-slides can be stored at warm room temperatures after sampling.
If no incubator is available, store the dip-slide after dipping in a warm location at about 72-75°F (22-24°C). Read the results after 36 hours.
If an incubator is available, use it at 30°C and read the results after 24 hours.
If waiting 36 hours before reading the results, interpretation of the resulting growth may become difficult, with individual colonies becoming indistinguishable from each other as the colonies grow larger and merge with adjoining colonies.