How do you create a schedule for a project with a gap period in the project contract

Hi All, please can anyone help. I am trying to build a schedule for a 3year contract that has a lump sum limited liability contract for the first 6months. The plan is to use these first 6months to finalise and approve the design which will then be used to define the rest of the project in detail. There are bound to be budget allocation delays between these first 6 months and the rest of the project, bit the exact duration of the delay is uncertain. How do I build such a schedule intended for EVM without this break point causing reporting issues? I hope my question is clear. Thanks