You can enter into a pre-nuptial agreement with your intended spouse/civil partner at any time prior to your wedding. However, we strongly recommend that you provide your future spouse/civil partner with sufficient time before the wedding to consider the proposed agreement and that signing occurs not less than three months before. In England and Wales, pre-nuptial agreements (following Vardags’ victory in Radmacher v. Granatino  UKSC 42) will be given effect upon divorce so long as they are fair. To determine whether your agreement is fair, the courts will look at various factors and will want to know that the agreement was “freely entered into by each party with a full appreciation of its implications”. Generally, both parties will therefore need to disclose their respective financial positions and will each need to obtain independent legal advice.
If you are running out of time and your wedding is looming, do not worry; you can enter into a pre-nuptial agreement prior to the wedding and a post-nuptial agreement (in the same terms) shortly afterwards.