Ideally, you should seal your driveway when there won’t be rain for several days, but at a minimum, there can’t be rain for at least 24 hours. If it rains shortly after you seal your driveway, the water can wash away the sealer and render your work useless. You’ll have to wait for your driveway to dry out and try applying again. Note that some sealers—like oil-based sealers or specialty fast-drying sealers—may cure faster. Ask your contractor for information on timing before the install, and if there’s rain in the forecast, postpone the job.