ooh start now!!

If your cover is lanolised properly it will not get compression leaks. You will need to relanolise every month or so, and wash the cover in wool wash by hand is best when ever it is actually soiled. After wear just air it out. Only need to wash wool covers when they are soiled or every month - when they are smelly - and then lanolise after washing.
There should be care instructions with it, or available form where you bought it.

Disanas are FABULOUS and wool is best for overnight, as it is both absorbant and water repellant at the same time - meaning any leaks of the Night Nappy it will soak up but the wool will not ever leak if lanolised properly. It also breathes, helping prevent nappy rash