Minimum Number of Hours Per Week and Minimum Number of Hours Per Working Day are not available on the Accounting Preferences.
In the accounting preferences, the other preferences for maximum hours restriction and minimum hour limit for time entry are available.
The preferences will show once the Advanced Approvals on Time Records are activated. To activate the preference, navigate to Setup > Accounting > Accounting Preferences > Time & Expenses > Time Tracking section > Advanced Approvals on Time Records = True