A coastal address does not prove that every part of a yard is sandy. Imported fill, beds and construction can create several growing conditions within one property. Keep notes by area so that one dry corner does not dictate watering for the entire lawn.
Check what the water reaches
UF/IFAS notes that sandy soils hold water for less time than soils with more clay. Inspect the rooting area and compare moisture after watering. Water that disappears from the surface is not automatically reaching the roots evenly. Use your local grass guidance to interpret what you find.
Check coverage before frequency
Walk the irrigation zone while it runs. A blocked head, a poorly aimed sprinkler or a windy edge can create a dry patch even when the soil elsewhere is wet. Mark the locations on a sketch; keep a record of the settings before making one change at a time.
Let a test guide nutrition
Ask a soil lab for recommendations for the grass you actually grow. Keep the report with the product label and lawn measurements, and avoid adding a fertilizer simply because the soil looks pale. Sand content alone does not establish a feeding rate. Revisit your notes after weather changes instead of treating the original schedule as permanent.
Do not extend every irrigation zone to compensate for one poorly covered corner.