Originally Posted by Voodoo Daddy

From the FAQ:

If I check-in before January 4, 2019, or check-out after May 5, 2019, do I still earn credit for that stay?
Registered Hilton Honors members will receive a bonus only for the nights of an eligible stay completed during the Promotion Period, regardless of a check-in date before the Promotion Period begins or a check-out date after the Promotion Period ends.

Your night would not be completed during the promotion period, so the way I read this, it would not count. However, it would appear that a stay from May 4 to May 6 would count as one night.