This is like timing flowering for the Chelsea Flower show- and is not an exact science and in a garden situation difficult
Get them planted now-if they are behind you can always try to speed them them up by bringing them into a warmer condition-but if they are ahead they would need cooler conditions to slow them down-not so easy
They should naturally flower in April but who knows what the weather conditions are going to be for the next 5 months?
It might be work for you -but on the other hand...............