This picture is from the English magazine Englishwoman's Domestic Magazine, and shows some models for both hats and hair in the year of 1869. It is from the May issue and thereby it can be determined that it is late spring-summer hats.
The difference between summer and winter is actually more in the colours than the models of the hats - since when have people bothered about practical fashion?
The difference between coiffures in the beginning of the 1860's and the later part of the same decade is actually quite great, though not many years differ. Earlier the hair had been very straight and tied back from the face in a rather severe fashion, any curls were at the back of the head, and in the day-time most of it was hidden by the bonnet. This was not the case any more.
The hair was still kept away from the face, but even there some waves in the hair was allowed, to give a softer look. Then the hair was gathered high up on the back of the head and long locks were hanging down there. It was definitely pinned up, as grown women were supposed to have it, but still more resembling how girls would wear their hair than it had in ages.
The hats and bonnets that came with these hair-dos were made to sit on top of these creations, without hiding them. Small hats and equally small bonnets were placed on the top of the head, sometimes even in front of the pinned up curls. This was more a symbol of head-wear than something that actually protect from the weather, which had been it's initial goal. But the head-wear had to be always present - pretty much without regard to the shape and size of the thing.