Some people try to use formulas to understand times that are described in Revelation. For example, they may use the formula that one day equals one year. They might conclude that one hour is 1/24th of a year (half a month, or about 15 days).
The problem here is that we have two time periods being used to describe what appear to be one event. In this verse her plagues come on her in "one hour." In verse 8, her plagues come upon her in "one day." The simplest interpretation is that time is not intended to be too precise. In other words, the term "one hour" is intended to mean suddenly and not 60 minutes. To attempt any other explanation seems too forced and complicated. A person would need to conclude that judgment (which comes in one hour) is something different from plagues (which come in one day). To take this position for this one issue, threatens to put in jeopardy all the other scriptures which equate plagues with judgment.