Work Towards a Given Date

To help a client focus their thinking, it helps to work towards a given date. They will normally be aware of an event for which they would like the site to be ready, and it helps to work backwards from this date.

For example: 

We need to allow three months to build and set up your platform. If you would like to showcase the site in March, we will need you to confirm the order by December, so that we can begin working to get your platform ready on time.