A long procedure cannot be assessed by one universal number of months or years. Article 6(1) ECHR requires a hearing within a reasonable time. The assessment considers the complexity of the case, the conduct of the applicant, the conduct of authorities and courts and the importance of the matter.
Start with a complete timeline. Record the application or claim, service, submissions, evidence, expert reports, adjournments and decisions. A case may be problematic even when it contains individual steps if the overall duration is no longer proportionate to its subject and importance.
State liability also requires section 1 AHG. An official acting in execution of the law must have caused damage to property or a person through unlawful and culpable conduct. Unreasonable duration is therefore one legal issue, not the whole claim.