Let’s assume that all the elements of min heap of n elements are distinct. So, the time required to find the Kth smallest element in min heap or Kth largest element in max heap, where K is independent of n will be O(1) as the Kth smallest element in min heap or Kth largest element in max heap will be present in the first K-levels (When given that we have access to the array elements)
Let’s say we have a min-heap of 127 elements, so the 5th smallest element will be present in first 5 levels. So, we need total 1 + 2 + 4 + 8 + 16 comparisons = 31 comparisons = O(1).
So, we need O(1) time.