Between a domain expiring and becoming available to the public to register, there is a period in which the current domain owner can renew or redeem their domain.
The length of this period and the cost of renewal (Grace period) or redemption depends on the domain type.
The registry requires a fee to be paid to retrieve a domain during the Redemption period. After this the domain is pending Deletion, before it drops and is available to register. It is common practice for the drop time to be randomised which can make it very difficult to predict exactly when domains will become available. Please contact support to enquire about a particular domain who can provide advice.