Original: The 921 earthquake, also known as the 1999 Jiji earthquake or simply 921, was a magnitude 7.6 earthquake which occurred at 1:47 local time (17:47 UTC) on September 21, 1999 in Jiji, Nantou, Taiwan.
Simplified: The earthquake happened on September 21, 1999 at 1:47 am local time (September 20 17:47 GMT).