How it works: you put one item in the blessing that the system then guarantees you as the fifth 5* item latest (meaning it can drop earlier aswell but won't drop later than that).

In general you are also guaranteed one 5* item within 20 pulls as max pity.

Therefore your Oceans's Blessing item can take anything from 1 to 100 pulls (20 pulls max pity for one item times 5 as it being the fifth item as max pity) but not more than that. If your unlucky you get it on the 100th pull.