You can accomplish this from Global Settings. Open the Global Settings from the company menu > Settings. Under the Time & Expenses panel, review the Time Entry section. Here, you can set the 'Time entry should not be saved/deleted if older/newer than...' rule for your company. Adjust as necessary for your pay period and click Save when you are done.
If you do not want this applied to all your employees, you can change the Global Settings to allow specific employees to bypass this setting. Open Security Permissions from the company menu > Settings. Select the employee you want to allow to bypass, such as a project manager, and change the permission for that person under the Time Entry section. Enable the option: Allow adjust date beyond global setting restriction. Click Save and you're all set!