Solar radiation heats land faster than water for multiple reasons, including the higher heat capacity of water, water's reflectivity and the more absorbent, textured surface of the earth. Water reflects solar radiation, while land absorbs the sun's heat because land is generally darker than water.
Darker surfaces like land absorb more heat than reflective surfaces, which send heat and radiation back into the atmosphere. Textured surfaces, such as land, also absorb heat more efficiently than flatter surfaces like water. The fluid molecular structure of water, in which water molecules move fluidly against each other, causes water to have a higher heat capacity than land, which has a solid molecular structure. Having a higher heat capacity means it requires more energy to heat the same volume of water than land.
Based on heat capacity alone, it takes longer to heat up the same volume of water than land. Having a higher heat capacity also means that the oceans store much more heat than land. They also store more heat than land because water covers more of the Earth's surface. Water temperatures fluctuate less rapidly than land temperatures, and oceans maintain approximately the same temperatures regardless of season and air temperature. The constant temperatures of the oceans maintain and regulate the overall climate of the Earth.