The two countries that are 24 hours apart are Samoa and American Samoa [1].

Samoa is located to the east of the 180° meridian, while American Samoa is located to the west of the 180° meridian. This results in a 24-hour time difference between the two countries [1].

Samoa follows the Samoa Time Zone (SST), which is UTC-11:00. The clock time in this zone is based on the mean solar time of the 165th meridian west of the Greenwich Observatory [3]. American Samoa, on the other hand, is one hour ahead of the Howland and Baker islands and 23 hours behind the Wake Island Time Zone [3].

It's important to note that the nation of Samoa used to observe the same time as the Samoa Time Zone until it moved across the International Date Line at the end of December 29, 2011. As a result, Samoa is now 24 hours (25 hours in southern hemisphere summer) ahead of American Samoa [3].

Learn more:

1. Which two countries are 24 hours apart? - Quora
2. What Is The Biggest Time Difference Between Two Places On Earth? - WorldAtlas
3. Samoa Time Zone - Wikipedia