These are set in the menu Administration | My Preferences in the web client. Note that there is no corresponding setting in the professional client.
There are three tabs with multiple sections under each to review and ensure they will affect scheduling in the way your organization prefers.
Even though these are user settings, they affect a schedule enough that they should be agreed upon and consistently used by all users in that database. A corporate standard should be documented and followed.
On the Global tab in My Preferences (web) or the User Settings (Optional Client/Pro), the following sections have an effect on scheduling:
A fundamental ...