I would tentatively agree that most spring breaks will happen before Easter in 2019.
The Deluxe AP Saturday blockouts begin on March 16, which would indicate that is about when they expect the Spring Break Season to begin. I'm not sure if the longer hours would start the Monday of that week or the Monday following the first Saturday Deluxe AP blockout. So it's possible that you might still have shorter hours and limited entertainment on the weekdays prior to the 16th.
At this point, the only event that I've heard about is Spring Dapper Days on April 13 and 14. That might mean larger crowds than "normal" during that weekend (although, all weekends during the Spring Break Season are likely to be busy). The Spring Break Season SoCal and SoCal Select AP blockouts start the weekend before Easter and run through Easter (4/12 or 4/13 through 4/21).
Personally, I would probably opt for dates close to the start of your April period. I thought seeing other guests in their Dapper Day best was fun. Also, it seems possible that the Easter Egg Hunt might be happening by then (it started about two weeks before Easter this year). Lastly, this is likely within the Spring Break season, so there should be long hours and full(er) entertainment even on the week days.