You can prevent financial entries prior to a user-specified date by going into File>Financial Configuration>Cutoff dates. There are three separate dates; each covering a specific area. These are:
- Order, Order Transactions, and Inventory
- Supplier Invoicing
- Customer Invoicing and Payments
For financial entries relating to future dates you should go into File>System Configuration>System Settings and enter a single value representing the maximum entry days forward that you are going to allow