The Account Owner and Admins can adjust the default work hours per day and work days per week from the Preferences tab within Team Settings.
If you need to adjust your team's capacity in the future or remove/add a work day, a new "Apply To" field will appear. There are two options for setting new hours and work days:
All past and future dates: This option impacts your team's past/future capacity. For example, reducing Friday from 8 hours to 4 hours will add overtime to any person who has more than 4 hours of tasks scheduled on a Friday.
Note: Unchecking a work day and selecting Update will delete all scheduled tasks on that day. This action cannot be undone.
A specific date onward: This option allows you to choose a date in the past or future to apply the changes. The date must be at the start of the week (Sun or Mon based on your settings). Using the example above, reducing your team's capacity on Friday from 8 to 4 hours during the summer will not impact any of their previously scheduled tasks, and you can increase the hours again when autumn rolls around.
Any changes you make to your team's work days or hours are displayed by clicking View changes.
To change an individual team member's work days/hours without impacting the rest of your team, check out this article.