The phrase "within a few hours" is correct and usable in written English. You can use this phrase when referring to a time period that is relatively short. For example: "I need to finish this project within a few hours.".
Within a few hours, he was dead.
"Within a few hours there was looting.
Within a few hours, the "massacre" ensued.
Within a few hours, bedlam broke out.
(Update: Hondros died within a few hours).
Millions of messages went out within a few hours.
Five soldiers died instantly and two within a few hours.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK