//There is no definitive answer to this question as all walls and ceilings will dry out at different speeds. With a normal centrally heated house you can be pretty sure of safely painting after 4 weeks but it can take as long as 6 and with extra heat in the room it may be ready in 3.
The reason for not painting before the wall is completely dry is that most paints will simply form an air tight skin over the wall. The moisture from the new plaster is then trapped behind this skin and cannot evaporate off. The damp then either retreats back into the wall where it develops mould growth or reacts with the salts in the wall to become Efflorescence. Either way you have a problem on your hands that is incredibly difficult to deal with.//
Think I would give it a couple of weeks at least Jenny. When the finish is almost white rather than deep pink is when I have always done it.
http://www.diydoctor.org.uk/projects/paintnewplaster.htm