I don't believe they extended the promo last year. As PP have said, you need to first use the ticket by the end of April.
They've offered this promo for several years now, and every year it has ended at the end of April.
For what it's worth, the first few days of May are far less crowded than the end of April. Most people are trying to take advantage of the lower ticket costs plus the nice spring weather and come into the park the last week of April.
We've been in early May a couple of times, and CM's have remarked each time how much quieter and emptier the park is in early May than the previous weeks.