JQL extensions allow you to search for issues depending on whether or not they currently have a timer running, or depending on their accumulated hours.
Find Issues with a Running Timer
Use the timerIsRunning extension to find issues that currently have a running timer. The example below will return all issues in the HC project that have at least one timer running.
Find Issues with Relative Accumulated Hours
The allTimersInHours extension returns a numeric value that can be used in relative expressions. The example below will return all issues in the HC project that more than 10 accumulated hours.
Find Issues by User and Timeframe
You can use the worklogAuthor and worklogDate fields with JQL date/time functions to return issues that have been worked on during a time period.
JQL Date/Time Functions