After leaving the plaster dome overnight to let it dry I took it out without a problem apart from the mould which I had cracked and had to replace

Before mixing the plaster for the mould I smoothed the dome to get the best finish on the dome and ensure I would get a perfectly round mould

I also made a wooden circle for the dome to sit on which created the size the mould needed to be

I am happy with the result of the mould and appears to be smooth which should prevent issues during future castings.