Users who belong to the group specified by the "timetrackinggroup" parameter have access to time-related fields. Developers can see deadlines and estimated times to fix bugs, and can provide time spent on these bugs.
At any time, a summary of the time spent by developers on bugs is accessible either from bug lists when clicking the "Time Summary" button or from individual bugs when clicking the "Summarize time" link in the time tracking table. The summarize_time.cgi page lets you view this information either per developer or per bug, and can be split on a month basis to have greater details on how time is spent by developers.
As soon as a bug is marked as RESOLVED, the remaining time expected to fix the bug is set to zero. This lets QA people set it again for their own usage, and it will be set to zero again when the bug will be marked as CLOSED.