Grazing incidence X-ray scattering was used to follow the microphase separation during room-temperature solvent annealing of films of high interaction parameter cylinder-forming 16 kg/mol polystyrene-b-polydimethylsiloxane block copolymer in a toluene heptane mixed solvent vapor. Microphase separation was observed for swelling ratios above 1.2, but swelling ratios above 1.9 caused the films to disorder. The films exhibited a thickness-dependent microdomain reorientation during annealing, with the initial out-of-plane cylinder orientation converting to an in-plane orientation as a result of preferential surface interactions. Drying led to a reduction in the out-of-plane cylinder spacing, with slower drying leading to greater deswelling and larger distortion of the hexagonal lattice.