The way you phrase your question is pretty complicated to understand. You seem to need to invoice based on the progress of the projects you conduct and that the timeframe of your projects vary from one another. If that's the case, you should probably look into contract invoicing which is made for that.

For this, install the "Contracts management" module, go to Sales > Contracts, and look at the "Invoicing" section of the contract. It will allow you to specified fixed amounts, variable amounts (time & material based on timesheets), and expenses. You will be able to manage the invoicing of your project based on project phases (2 or 4 weeks in your example).

Hello Frabice, yes, I have unfortunately a bit unclear. Unfortunately my english is not so good. I will try to do it again. Under accounting- >Configuration- >Payment terms I have the template 15 days changed so that the payment of the deposit is to contribute immediately. In the final payment I have here a set period of 30 days. This deadline of 30 days but will be replaced by the date of delivery of the order confirmation - 2 days. I would like to customer loyalty that the customer sees the following on his order confirmation, if the order e.g. The 03.17.2013 is used as the date of delivery: payment: a deposit immediately, final payment until the 3.15.2013 .