For your first several watering cycles, Greg is in “learning mode.” Your habits and intuition about your plants’ needs are being combined with Greg's existing encyclopedic knowledge—all to give you the most accurate recommendations for each plant as time goes on.
If you feel your plant needs water before Greg suggests it, you can always water a plant early by visiting the Upcoming tab and swiping right on your plant, or selecting it in the plant grid and choosing the Water option.
It’s important to do this so Greg will learn to suggest that plant for water more frequently in the future. After Greg's initial learning period, your watering recommendations should fit you and your plants like a glove!