Painting a new house sounds easy: clean surfaces, no old paint, nothing to repair. In practice, new work is less forgiving than a repaint.
Bare plasterboard and fresh render are porous and absorb paint unevenly. They must be sealed first, and a sealer is not a first coat of wall paint. Skip it and the joints show through at a different sheen, a defect that cannot be fixed without starting again.
Fresh render is alkaline and holds moisture, so it needs time before coating. When a build programme slips, this is where the pressure lands, and where it should be resisted.