Even when the plaster appears to be dry it’s not advisable to paint/tile a full float & skim (which I assume yours is) for at least 4 weeks, preferably 6. Even then it will still have fairly high moisture content, more so if you’ve suffered damp in the fabric. The best time to move into a new house is around April so you won’t need the c/heating on & the building fabric will have around 5-6 months to dry out naturally instead of being forced by c/heating. Such houses will usually suffer far less from shrinkage cracks which can appear at any time, sometime 2 or more years later as the timber dries out & shrinks as well.
A de-humidifier doesn’t provide heat; it removes moisture from the air. Reducing the ambient moisture content will encourage moisture in the building fabric to evaporate & migrate into the dryer air, so speeding up the process. I wouldn’t think this would cause too many problems if just relying on natural summer air temperatures but I suspect you also have the central heating on at the moment; this is far more likely to cause problems especially if used in conjunction with a humidifier.
That’s the theory but unless your suffering unduly from condensation I would leave it alone to dry naturally for at least 4 weeks from the time it went on. You can get breathable Trade Matt which is supposed to be suitable for green plaster but I have no idea if it stays on there in the longer term. I’m not a pro painter/decorator I just slap mud on but for my own work, I always leave it to do its own thing; why rush & risk ruining it!
I also think the previous advice you were given is sound & so hope this makes things clearer for you.