Inheritance valuation timeline

Quick question, after a person has passed away, my understanding is there needs to be independent certified appraisal on the fair value of the property left subject to inheritance . My question is within what time frame such appraisal needs to be done. Searching on the forums, it says as soon as possible. Could such appraisal be done let say within 6 months from the time of death? In addition, just to confirm, such valuation should be based on the date of death, correct? Thank you in advance