Probably best to leave by 6:30 at the latest on a weekday, 7 on a weekend. For weekdays leaving earlier will also make the drive quicker...once you get past mililani or so there isn’t much chance for any kind of traffic in the early morning unless the surf at waimea is huge (20 ft +) or one of the pipeline surf events is running. If you want to take as little risks as possible, leave early and either pack a breakfast the night before (and eat at a beach) or find someplace that is open from early in the north shore to eat at.