When the Order Management configuration setting is enabled, you have the opportunity to decide whether your Sales Invoices will be generated with the Sales Order's Order Date of the Sales Invoice's Created Date as it's Invoice Date. 

Update the Default Invoice Date in your Company settings

1. From the main menu, go to Settings and select Company.
   
   
2. In the Company page, go to the Invoicing tab.
   
   
3. Use the Default Invoice Date drop down menu to select either Created Date or Order Date.
   
   
   
4. Once selected, click Save. 

Any new invoices created for a Sales Order will then use the Default Invoice Date selection to populate the invoice's Invoice Date. 
NOTE: The Invoice Date can be manually updated per Sales Invoice, whilst it's in Parked status.