Original: Later that day, it was upgraded to Tropical Storm Darby, and only four hours later, at 2 a.m. (0900 UTC) on July 27, was upgraded to Hurricane Darby.
Simplified: Later that day, it was upgraded to Tropical Storm Darby, and only four hours later, at 2 am (0900 UTC) on July 27, is upgraded to Hurricane Darby.