There's no harm in postponing decoration for a while, in fact it will give the plaster time to dry out fully and any subsequent shrinkage cracks can be filled before painting. The only downside in a kitchen area is the risk of grease spots and splashes which would resist a subsequent water based paint. But these can easily be removed using a sugar soap solution. It's a good idea to wash all new walls down before decoration using a damp (not sodden) cloth (an old towel works well), rinsing regulary and leaving to dry for a couple of hours before painting. This will remove any dust and powdery residues from the new plaster surface.