Suggestion: Issue Tracker can have an checkbox per comment for optional time record entry. if you associate a task with an issue (up for a vote too!) , then this can implemented too. However, You will also a method of associating time records to issues and tasks (if not associated already). If the time records was associated with a task or issue, that time record could only be adjusted from the originating task or issue. Cool beans!

Will be great to report how much time consumed on Issues in order to charge customers properly. IT should be easy to implement