According to IMDB, May 28, 1982 was when Leonard Maltin joined Entertainment Tonight as movie reviewer; Wikipedia says May 29. We're going with Friday, May 28, because why wait another day to celebrate?
Unfortunately, clips of Maltin's review segments are hard to find online, but here's one from 1985:
Maltin's segment was the highlight of the show for me. I liked his 1-10 scale, which I think was uncommon for critics back in the day, and it was great when he did that slight pause before announcing his rating for a movie.