That is exactly when they do that. Once the application reaches the visa office, they check for missing documents or anything they need to continue with the process. For example, the proper marriage certificate, or the right birth certificate. If everything is there and they don't really need anything, they start assessing the eligibility, which means they will decide if they think the relationship is genuine. If they have concerns, they will schedule an interview. If their assessment is positive, they will proceed with doing other parts of the process, like criminality, background check, security checks, etc.