Do you see the point I'm making, though?

Edit: I'm not asking about the rate at which paid leave builds up, I'm asking about how the employee can ever be said to have used it up. Given that zero-hours contracts are a Bad Thing, I don't expect this to make any sense.

If I have accrued 24 hours of paid leave, and potentially work 6hrs a day, typically one day a week, do I need to pre-emptively use all of those 24 hours just to take leave for a block of 4 weekdays? It seems like I might have to, in the face of an unscrupulous employer.