Birthday and work anniversary messages are sent at 9:00 am based on your workspace's time zone setting.
Who can use this: Workspace Owners and Admins on the Basic plan and above, or on any plan during the free trial. Works the same for Slack and Microsoft Teams workspaces.
For an overview of the whole feature, read the Celebrations Guide.
By default, celebrations that fall on a weekend are shared earlier, on the previous Friday. You can choose to share them on the actual day instead.
Adjusting Celebrations Delivery Time
Go to the Web App.
Go to Settings, then the Celebrations section.
Click Advanced Settings.
Under Celebrations Delivery, click the dropdown and choose either:
Send on Weekdays shares them on the previous Friday.
Send on Weekends (actual day) shares them on the actual day, including weekends.
Click Save at the bottom to confirm changes.
Note: Reminder notifications for Admins and managers ahead of upcoming celebrations are also under Advanced Settings. See Celebrations reminder notifications.