Auto Update Milestone Commercials

When a project is created I need to update a field called "Invoice Due" in a Milestone called "Delivery" with the "Fixed Price" value.  It only needs to happen once as the amount may change when the project is built.

I've created a WF at the milestone level as follows:

• Only When a Record is Created
• Run only when the following conditions are met:  $Name="Delivery"
• Update Field:$C_InvoiceAmount = $FixedPrice

All of our projects are created by template, which I assume means the Milestone isn't actually created?

Thanks for any help