For each objective instance that will be created for a case, you must analyze the rules for deciding at which points in the case lifetime the case is entitled to the objective.
Whether or not a particular objective has been attained can vary over time - e.g. an allowance payable whenever a parent is absent from the household will be attained when a parent leaves and will cease to be attained once the parent returns; if the parent leaves and returns many times over the case's lifetime, then the case's entitlement to the objective will similarly vary many times.
For some simple products, the case is always entitled to an objective by dint of the case being eligible for that period of time, and thus there is no real entitlement calculation required. For other more complex products, the rules for entitlement to a given objective can rival those for overall case eligibility in terms of their complexity. It can be useful to have an understanding of the relative complexity of your overall case eligibility rules vs. the entitlement rules for your various objective types.
You must also analyze the requirements for the target of each objective instance, and any useful related reference information. The Engine allows the values these to vary over time, but for typical products the values are constant.