How to rotate log files based on time rather than size in Log4j?

I use Log4j with the RollingFileAppender to create a log rotation based on size.

How can I configure it to log to each file for a certain amount of time before rotating?

For example, so that each log file contains one hour of logs, rotating at the top of each hour?

I configure Log4j programatically in Java using a Properties object (as opposed to a log4j.properties file)