Short answers, pulled from the story.
The Japanese invasion of Thailand began on the 8th of December 1941. It took place roughly two hours before Japan's attack on Pearl Harbor, though the international date line places the two events on different calendar days.
Fighting during the Japanese invasion of Thailand lasted only about five hours despite fierce combat in southern Thailand. It ended in a ceasefire after Prime Minister Plaek Phibunsongkhram agreed to Japan's demands.
Plaek Phibunsongkhram was Thailand's prime minister during the Japanese invasion of Thailand. He could not be located when the invasion began and only ordered a ceasefire once he reached Bangkok.
Japan landed troops at Chumphon, Nakhon Si Thammarat, Prachuap Khiri Khan, Samut Prakan, Surat Thani, Pattani, and Songkhla, alongside a land crossing into Phra Tabong Province from Indochina.
The outcome of the Japanese invasion of Thailand was a formal alliance between the two countries, signed on the 21st of December 1941, making Thailand part of the Axis until the end of World War II. On the 25th of January 1942, Thailand declared war on the United States and the United Kingdom.
Seni Pramoj was Thailand's ambassador to Washington, D.C. after the Japanese invasion of Thailand. He refused to deliver Thailand's declaration of war against the United States and instead organized the Free Thai Movement.