I do not think they will postpone mediation. You don’t actually need an attorney for mediation. There are no lawyers allowed. It is just you, your ex, and a mediator. Mediation is a way for the two of you to reasonably work out your custody and visitation issues. Its actually a much more open forum than a court trial. And you don’t have to agree to anything in mediation you are not comfortable with. If it is your first scheduled mediation, you will actually only be going through an orientation session that explains coparenting and the mediation process. At the end of the orientation, the mediator then schedules you and your ex for your actual mediation appointment to sit down with the ex and mediator to try and work out a reasonable agreement.
I know it all seems scary, but it’s not anything to stress over.