When Wizard has a heart level of 5 or more hearts, you can ask him to go on a date with you. You must go to Wizard's house in Harmonica Town to ask him, and you must ask him before noon. If Wizard wants to go on a date, a scene will play where Wizard will ask to meet with you later. It's your choice if you'd like to accept, or to decline. If you're going to meet Wizard, he'll ask you to meet him at the Celesta Church Plaza at 16:00.
When you arrive, the two of you will wait for the stars to come out so you can look at them later. Wizard is a huge fan of astrology, and is excited to see the stars. He asks if you like stars too. Telling Wizard that you love them will increase his affection and continue the date. At the end of the evening, he will thank you for the time you've spent with him, and you will then go home.
Standing Wizard up for the date or declining his request for a date will result in losing heart points.