You can filter out weekends, holidays, and other times during which your team might not be working on your board's project(s).
This feature is available in GreenHopper 6.1.1 and later versions.
To specify working days,
If your team has a different time zone to the server, select the team's Time Zone.
In Standard Working Days, select all the weekdays on which your team typically works.
In Non-Working Days, click Add Date to specify holidays or one-off dates on which your team will not be working.
To remove a Non-Working Day, click the 'x' next to the date (see screenshot below).
These settings will be reflected in your Burndown Chart.
Screenshot 1: the 'Board Configuration' screen — 'Working Days' tab