This name is used to identify your company / account. It can be changed later under Options >> Settings & Defaults. This name will show up on system generated emails and on the login page. For example, Pelago or John's Little Web Shop.
Your account comes with a custom domain you'll use to log into Intervals (example: pelago.timetask.com). You can change this later if needed.
The time zone is used whenever a new person is created, but each person can select their own time zone for convenience.
Why does this matter? Locale affects how dates, times, numbers, and currency are displayed. This information can easily be changed later in the Settings & Defaults section.