After an insertion, you need to update the balance factor of each "parent" all the way up the tree until the root; so it's a max of O(log n) updates. But you will only have to do a single restructuring to restore the tree to it's invariants.
After a delete, like insertion, you will have to update the balance factor all the way up the tree; so again it's O(log n) updates. But, unlike insert, you may have multiple restructuring rotations to restore the tree to it's invariants.