Drying wood requires that water in the wood evaporates, and evaporation requires energy. There is a lot more energy available in the warm summer than the cold winter. However, summer can also be a lot more humid, so despite lots of available energy, some of the time the air doesn't have a lot of extra capacity to absorb moisture and evaporation can be slow. Still, on balance there is more potential for evaporation in summer than winter no matter where you live, even in humid climates. This is certainly true of evaporation from something like a pond where the water is in contact with the air and there is an unlimited supply of water. The situation with wood is a little different, since the water is closely held in the wood cells or intersticial spaces between wood cells, but I think wood is likely to dry better in summer, as long as you have a decent place to store it (not too damp in summer, not too shady, not tightly enclosed, etc.) Now if you happen to live in a spot where it is always calm in summer and always windy in winter, that might tip the balance, and I could probably think of some other exceptional situations, but for most of us I think summer means faster wood drying. I have not actually tested this, and i don't really pay close enough attention to say I have observed it, so this is just speculation.
Also, I don't think oak dries fast winter or summer, so my response to the original question about whether oak can go from 25 to 35% moisture content to 20% in a few weeks is I don't think so.
