Definitely not.
Prenups signed days before a wedding pose a huge risk of the financially weaker spouse later arguing they were pressured into signing. It is a red flag that the financially weaker spouse was given no choice but to sign the agreement and that the wedding would have been cancelled had they not signed.
If you have engaged a lawyer to prepare a prenup for your spouse to sign, then they should be given adequate time to review the agreement and your financial disclosure, obtain advice from their own independent lawyer and negotiate any changes to the terms. If they are not, this may constitute grounds to have the agreement set aside in the future.
Ideally, we recommend spouses entering a financial agreement have it prepared, negotiated and signed well before wedding plans are finalised and invitations sent out. This is because the process of preparing and negotiating the terms of a financial agreement generally takes months, not days.
In the case of de facto couples who may be looking to move in with each other or reach two years of living together, they would ideally see a family lawyer at least six to nine months before these milestone dates.
A financial agreement can still be made after marriage in the same terms as a prenuptial agreement. The financial agreement would simply need to refer to a different section of the Family Law Act; section 90B for agreements made in contemplation of marriage and section 90C for agreements made during marriage.
The same goes for de facto relationships; section 90UB for couples contemplating entering a de facto relationship and section 90UC for couples in a de facto relationship.
Signing a financial agreement after marriage is certainly a safer option where the wedding date is only days or weeks away. If the wealthier spouse considers a loss of their bargaining power (noting they need to be careful about communications with their spouse to avoid any suggestion they are pressuring them into signing the agreement), it is imperative they see an expert family lawyer at the earliest opportunity and months before their wedding.